The present Form of the Surface of the Earth
explained, with a View of the Operation of
Time upon our Land.
It is not to common observation that it belongs to see the effects of time, and the operation of physical causes, in what is to be perceived upon the surface of this earth; the shepherd thinks the mountain, on which he feeds his flock, to have been always there, or since the beginning of things; the inhabitant of the valley cultivates the soil as his father had done, and thinks that this soil is coeval with the valley or the mountain. But the man of scientific observation, who looks into the chain of physical events connected with the present state of things, sees great changes that have been made, and foresees a different state that must follow in time, from the continued operation of that which actually is in nature.
It is thus that enlightened natural history affords to philosophy principles, from whence the most important conclusions may be drawn. It is thus that a system may be perceived in that which, to common observation, seems to be nothing but the disorderly accident of things; a system in which wisdom and benevolence conduct the endless order of a changing world. What a comfort to man, for whom that system was contrived, as the only living being on this earth who can perceive it; what a comfort, I say, to think that the Author of our existence has given such evident marks of his good-will towards man, in this progressive state of his understanding! What greater security can be desired for the continuance of our intellectual existence,—an existence which rises infinitely above that of the mere animal, conducted by reason for the purposes of life alone.
The view of this interesting subject, which I had given in the first part, published in the Transactions of the Edinburgh Royal Society, has been seen by some men of science in a light which does not allow them, it would appear, to admit of the general principle which I would thereby endeavour to establish. Some contend that the rivers do not travel the material of the decaying land;—Why?—because they have not seen all those materials moved. Others alledge, that stones and rocks may be formed upon the surface of the earth, instead of being there all in a state of decay. These are matters of fact which it is in the power of men who have proper observation to determine; it is my business to generalise those facts and observations, and to bring them in confirmation of a theory which is necessarily founded upon the decaying nature and perishing state of all that appears to us above the surface of the sea.
Nothing is more evident, than that the general effect of mineral operations is to consolidate that which had been in an incoherent state when formed at the bottom of the sea, and thus to produce those rocks and indurated bodies which constitute the basis of our vegetable soil; but, that indurating or consolidating operation is not the immediate object of our observation; and, to see the evidence of that operation, or the nature of that cause, requires a long chain of reasoning from the most extensive physical principles. Our present subject of investigation requires no such abstract distant media, by which the effect is to be connected with its cause; the actual operation in general is the object of our immediate observation; and here we have only to reason from less to more, and not to homologate things which may, to men of narrow principles, appear to be of different kinds. But even here we find difficulty in persuading those who have taken unjust views of things; for, those who will not deny the truth of every step in this chain of reasoning, will deny the end to which it leads, merely because they are not disposed to admit the progress of that order which appears in nature.
In the last chapter, I have been using arguments to prove that M. de Luc has reasoned erroneously, in concluding the future stability of a continent; and I have been endeavouring to show that our continent is necessarily wasted in procuring food to plants, or in serving the various purposes of a system of living animals. We have now in view to illustrate this theory of the degradation of the surface of the earth; a theory necessarily leading to that system of the world in which a provision is made for future continents; and a theory explaining various natural appearances which otherwise are not to be understood. A door may thus be opened for the investigation of natural history, particularly that which traces back, from the present state of things, those operations of nature which are more immediately connected with what we take much pleasure to behold, viz. the surface of the earth stored with such a variety of beautiful plants, and inhabited by such a diversity of animals, all subservient to the use of man.
There are two ways in which we may look for the transactions of time past, in the present state of things, upon the surface of this earth, and read the operations of an ancient date in those which are daily transacted under our eye. The one of these is to examine the soil, and to trace the origin of that which we find loose upon the surface of the earth, or only compacted by the soft and cohesive nature of some of its materials. In thus studying the soil we shall learn the destruction of the solid parts; and though, by this means, we cannot form an estimate of the quantity of this destruction which had been made, we shall, upon many occasions, see a certain minimum of this quantity which may perhaps astonish us.
The second method here proposed, is to examine the solid part of the earth, in order to learn the quantity of matter which had been separated from this mass. Here also we shall not be able to compute the quantity of what had been destroyed; but we shall every where find a certain minimum of this quantity, which will give us an extensive view with regard to the operation of the elements and seasons upon the surface of this earth. We shall now examine more particularly those two ways of judging with regard to the operations of time past, and the changes which have been made upon the surface of our land, by those active causes, which, being in the constitution of this earth, must continue to operate with undiminished power, and tend to preserve the whole amidst the destruction of its particular parts.
The quality of the soil or travelled earth of the globe is various; because the solid parts, from the destruction of which the soil is formed, consist of very different substances, in the different portions of each country. Thus, in one part of a country, the soil will be calcareous, or containing much of that species of substance; in another, again, it will be argillaceous; in another sandy, where the prevailing substance is siliceous. These are the original soils; other substances may be considered as adventitious to this soil, though natural to the surface of the earth, which is covered with plants and animals. The substance of those animal and vegetable bodies, mixed with the soil, adds greater fertility to the earth, and gives a soil which is still more compounded in its nature, but still composed of those materials now enumerated.
We have been now supposing the solid parts below, or in the same field, as furnishing materials of which the soil is formed; this soil then partakes of the nature of those solid parts, whether more simple or more compound. There is, however, another subject of variety, or still greater composition in soils; this is the transportation of materials from a distance; and this, in general, is performed by the ablution of water, in following the declivity of the surface. But sand is sometimes travelled by the wind, and proceeds along the surface of the earth, without regard to the declivity, and changes the nature of soil in those places which happen to be exposed to this accident.
There cannot be any extensive, great, or distant travelling of sand or soil by means of the wind, except in those places which are sterile for want of rain, and thus are destitute of rivers and of streams; for, these running waters form every where a bar to this progressive movement of the soil, even if the sterility or dryness should permit the blowing of the sand. But the operation of streams and rivers, carrying soil and stones along the surface of the earth, is constant, great, and general over all the globe, so far as a superfluity of water, in the seasons of rain, falls upon the earth.
From the amazing quantity of those far travelled materials, which in many places are found upon the surface of the ground, we may with certainty conclude, that there has been a great consumption of the most hard and solid parts of the land; and therefore that there must necessarily have been a still much greater destruction of the more soft and tender substances, and the more light and subtile parts which, during those operations of water, had been floated away into the sea. This appears from the enormous quantities of stones and gravel which have been transported at distances that seem incredible, and deposited at heights above the present rivers, which renders the conveyance of those bodies altogether inconceivable by any natural operation, or impossible from the present shape of the surface. This therefore leads us to conclude, that the surface of the earth must have been greatly changed since the time of those deposits of certain foreign materials of the soil. Examples of this kind have been already given. I shall now give one from the Journal de Physique.
«Les bords du Rhône aux environs de Lyon, et sur la longueur de quarante lieues, et de plus, des montagnes entières, dans le même pays, sont formes de pierres dont on ne trouve les analogues que dans la Suisse. Ce fait presqu'incompréhensible est accompagné de beaucoup de circonstances qui méritent d'être détaillées dans un discours plus longue que celui-ci. Il y a cependant une que je ne peux pas m'empêcher de rapporter ici, comme une suite de ce que je viens de dire.
«Dans cette grand catastrophe, à laquelle j'attribue le transport de ces matières alpines, il se fit de grandes échancrures dans le Jura; les plus profondes que j'aie vues sont celles de Jougue de Sainte-Croix, du val de Mousthier Travers, de Someboz au val de Saint-Inver, une cinquième aux environs du village de Grange, trois lieues plus bas que Bienne, et une sixième à quatre à cinq lieues plus bas que Soleure, à l'endroit dit la cluse. Cette dernière est la plus profonde, et se trouve de niveau avec les eaux de l'Aar. Beaucoup de ces matières étrangères au Jura, ont passé par ces échancrures, et sans doute, par bien d'autres et se sont répandues, dans plusieurs de ces vallées. J'en ai vu un suite bien marquée qui a passé par Jougue, par Saint-Antoine, part Mont Perreux, les Grangettes, les Granges Friards, Oye, et qui est allée jusqu'aux plaines de Pontarlier. Cette suite est en ligne droite vis-à vis l'échancrure de Jougue, et la direction de la vallée qui est au bas de ce village. On en trouve quelques morceaux à Metabiefs, mais je n'en ai point vu aux Longevilles, ni à Roche-Jean. Il y en a au-dessus de Saint-Croix ou d'autres ont pu passer aussi pour aller de même aux environs de Portarlier. Il y en a dans le val de Mousthier-Travers jusqu'au dessus de village de Butte; elles ont même passé les roches de Saint-Sulpice du côté des Verrières de Suisse, ou l'on a été obligé d'en faire sauter de gros blocs avec de la poudre pour dégager la grande route; il y en a dans les vallées de Tavannes, et de Delemont; on en trouve bien plus loin, j'en ai vu près de Roulans, et je ne douterois pas que les pierres meulières de Moissez et des environs n'eussent la même origine.»
M. de Saussure, who has so well observed every thing that can be perceived upon the surface of the earth, gives us the following remarks which are general to mountainous countries. (Voyages dans les Alpes, tome 2d § 717).
«Dans le haut des vallées entourées de hautes montagnes, on ne voit point de cailloux roulées, qui soient étrangers à la vallée même dans laquelle on les trouve; ceux que l'on y rencontre ne sont jamais que les débris des montagnes voisines. Dans le plaines au contraire, et à l'embouchure des vallées, qui aboutissent aux plaines et même assez haut sur les pentes des montagnes qui bordent ces plaines, on trouve des cailloux et des blocs que l'on diroit tombés du ciel, tant leur nature diffère de toute ce que l'on voit dans les environs.»
Here are facts which can only be explained in supposing that the valleys have been hollowed out of the solid mass, by the gradual operation of the rivers. In that case stones, travelled from a far, will be found at considerable heights, upon the sides of the valleys at their under end, or where, as our author says, they terminate in plains.
We have a striking example of the operation of time and the influences of the atmosphere, in wasting the surface of the rocks, and forming soil upon the earth; this is the kaolin of the Chinese, or the true porcelain earth, which is the produce of granite countries. The feldspar of the granite rock exposed to the atmosphere is corroded very slowly indeed, by the effects of air and moisture, and in having the soluble earth or calcareous part of its composition dissolved; the surface of this stone, thus, in a long course of time, becomes opaque in having the white siliceous earth exposed to view, and thus appears like a calcined substance. The snows and rain detaches from this surface of the rock the white earth, which being deposited in the plain below, forms a stratum of kaolin more or less pure, according to the circumstance of the place.
As this operation of the atmosphere upon the surface of granite is so extremely slow as to be altogether unmeasurable to man; and as there are in many places of the earth inexhaustible quantities of this kaolin, notwithstanding a small portion only of the ablution of the rock had been retained upon the surface and deposited by itself, it must appear that much time had been required for amassing those beds of kaolin, and that these operations, which in the age of a continent is nothing, or only as a day, are, with regard to the experience of man, unmeasurable.
For approbation of this theory, it is not necessary to show, that wherever there is granite found, there should be also kaolin observed; but it is necessary that wherever kaolin is found, there should be also granite or feldspar to explain its origin; and to this proof the theory is most willingly submitted. The following are the places which have come to my knowledge. First Loch Dune in the shire of Ayr; this lake receives its water from the granite hills which are at its head. Secondly, some small lakes which receive the washings of the granite mountain, Crifle, in East Galloway. Thirdly, Cornwall, a county in which I have not been, but which is sufficiently known as possessing kaolin and granite.
Another example from a very distant country we have both from M. Pallas, in the Oural mountains, and from M. Patrin, who has given a mineralogical notice of the Douari, Journal de physique, Mars 1791. Here we find the following observation.
«Parmi les chose intéressantes qu'offrent les rives de Chilea, on remarque au dessous de la fonderie, des collines de petunt-fé blanc comme la neige, parsemé de mica argentin de la plus grande ténuité. Dans le voisinage de ce petunt-fé est une argile micacée, qui en est peut-être une décomposition: on essaya en ma présence d'en faire de la poterie qui avoit tous les caractères du meilleurs biscuit de porcelaine.»
We have now been endeavouring to illustrate the wasting and washing away of the solid land, in the examples of decayed rocks and water worn stones, all of which are traceable, though at a great distance, to their source; we are now to consider another species of substance, which is still more particular as to the place of its production, or to its original situation, this being only in the veins of the earth. Among all the various productions of mineral veins, we have only now in view some particular metallic substances which do not seem to waste and be dissolved, as many of them are, in being long exposed to the influence of air and rain. When, therefore, the solid parts of the land are wasted in time, and carried away from the surface of the earth, the contents of the veins, which are occasionally found in those decayed parts of the land, are also carried away in the stream; but as the specific gravity of those metallic contents is much greater than the other stony materials moved in the stream, they sink to the bottom, and tend much more to be deposited upon the land, than those stones which had moved with them from their place. Hence it is, that deposits, rich in those metallic substances, are formed in certain places of the soil; and these are sought for, upon account of the value of their contents. Thus, stream tin, which in the time of the Romans formed a subject of traffic, is still found in the soil of Cornwall, even in great profusion, at this day.
Nothing can tend more to illustrate this travelling of the wasted surface of the solid land, than the contents of those mineral veins suffering in the general destruction of things, but partly saved from that total ablution by which so much of the solid parts had been made to disappear; and nothing can, in a more beautiful manner, show this order of things, than the method practised by the Cornish miners in quest of the original country of that metal, by shoding, (as it is called) upwards in running back the tract in which the stream tin had been conveyed. This is done by trying parcels of the soil, in always mounting to see from whence the mineral below had come.
Gold is thus found almost in every country but it is only in the most sparing manner that it may thus be in general procured, by reason of the few veins in which gold is found, and the small quantity of this metal contained in those veins. America, however, affords an example of veins rich in gold, and it is also there that quantities of stream gold is found in the soil, bearing a due proportion to the number and riches of the veins.
I shall give an example concerning the situation in which this stream gold is found in Peru (Voyage au Pérou, par M. Bouguer, page 49.)
«Cette Cordelière occidentale contient beaucoup d'or de même que le pied de l'orient, et celui d'une autres chaîne très-longue qui s'en détache un peu au sud de Popayan, et qui après avoir passé par Santa Fé de Bogota, et par Mérida, va se terminer vers Caracas sur la mer du nord; outre que l'or en paillettes occupe toujours des postes assez bas à l'égard du reste de la Cordelière, on ne peut aussi jamais le découvrir qu'en enlevant presque toujours deux couches de différentes terres qui le cachent. La première, qui est de la terre ordinaire, a trois ou quatre pieds d'épaisseur et quelquefois dix ou douze. On trouve souvent au dessous une couche moins épaisse qui tire sur le jaune, et plus bas est une troisième qui a une couleur violette, qui a souvent trois ou quatre pieds d'épaisseur, mais qui n'a aussi quelquefois qu'un pouce, et c'est cette troisième dans laquelle l'or est mêlé. Au dessous la terre change encore de couleur, elle devient noire comme à la surface du sol, et elle ne contient aucun métal. D'ailleurs on ne creuse pas indistinctement par tout. On se détermine à chercher en certains endroits plutôt qu'en d'autres par la pente de terrain. On agit comme si l'or avant que d'avoir été couvert par les deux couches supérieures, avoit été charrié par des eaux courantes. On s'est assuré aussi que les terres une fois lavées ou dépouillée de leurs richesses n'en produisent point d'autres; ce qui prouve que l'or y avoit été comme déposé.»
Therefore, whether we consider the quantity or the quality of the materials which are found composing the soil upon the surface of the earth, we must be led to acknowledge an immense waste of the solid parts, in procuring those relicts which indicate what had been destroyed.
We have now to examine what is left of that solid part which had furnished the materials of our soil; this is the part which supports the vegetable or travelled earth, and this earth sustains the plants and animals which live upon the globe. It is by this solid part that we are to judge concerning the operations of time past; of those destructive operations by which so great a portion of the earth had been wasted and carried away, and is now sunk at the bottom of the sea.
Man first sees things upon the surface of the earth no otherwise than the brute, who is made to act according to the mere impulse of his sense and reason, without inquiring into what had been the former state of things, or what will be the future. But man does not continue in that state of ignorance or insensibility to truth; and there are few of those who have the opportunity of enlightening their minds with intellectual knowledge, that do not wish at some time or another to be informed of what concerns the whole, and to look into the transactions of time past, as well as to form some judgment with regard to future events.
It is only from the examination of the present state of things that judgments may be formed, in just reasoning, concerning what had been transacted in a former period of time; and it is only by seeing what had been the regular course of things, that any knowledge can be formed of what is afterwards to happen; but, having observed with accuracy the matter of fact, and having thus reasoned as we ought, without supposition or misinformation, the result will be no more precarious than any other subject of human understanding. To those who thus exercise their minds, the following remarks may furnish a subject for some speculation. Now, though to human policy it imports not any thing, perhaps, to know what alterations time had made upon the form and quantity of this earth, divided into kingdoms, states, or empires, or what may become of this continent long after every kingdom now subsisting is forgotten, it much concerns the present happiness of man to know himself, to see the wisdom of that system which we ascribe to nature, and to understand the beauty and utility of those objects which he sees.
There are two different operations belonging to the surface of this globe which we are now to consider, and by which we shall be enabled to form some computation of what had been in space and time, from that which now appears. Moving water is the means employed in both those operations; but, in the one case, it is the water of the sea; in the other again, it is the water of the land. The effect of the one operation is the wasting of the coast, and the diminution of that basis on which our land and soil depends; of the other, again, it is the degradation of our mountains, and the wasting of our soil. In the course of this last operation, there is also occasionally land formed in the sea, in addition to our coast.
With regard to the wearing of the coast by the agitation of the waves, this is an operation of which some understanding is to be formed from the surest of all records, from a careful examination of our shores which are in this decaying state, and by observing what has been removed from those portions which we find remaining. Few people have either the skill or the opportunity of thus judging of the state of our earth from that which actually appears; but there is no person, who studies this science of geology, that may not satisfy himself with regard to the truth of this theory, by looking into our maps and charts, and making proper allowances for causes which cannot appear in the maps, but which may be understood by a person of knowledge making observations on the spot. In order to assist this study, the following observations may be made.
It is a general observation among mariners, that a high coast and rocky shore have deep water; whereas a low coast, and sandy shore, are as naturally attended with shallow water. The explanation of this fact will appear by considering, that a steep rocky coast is occasioned by the sea having worn away the land; and, when that is the case, we are not to expect sand should be accumulated upon that shore, so as to make the sea shallow. Look round all the coasts of Great Britain and Ireland that are exposed to the wide ocean, as likewise those of France and Norway, deep water, and a worn coast, are universally to be acknowledged. If again the coast is shallow, this is a proof that the land affords more materials than the sea can carry away; consequently, instead of being impaired, the coast may here increase and be protruded from the land. Such is the case in many places along the coast of North America, where several reasons concur in accumulating sand upon that coast; for, not only is the shore plentifully provided with sand from the rivers of that continent, but also the sand of the Mexican Gulf would appear to be carried along this coast with the stream which flows here towards the north, and which has thus contributed to form the banks of Newfoundland.
The second general observation is to be considered as respecting the shape of coasts, in like manner as the first had in view their elevations. Now, it is plain that the shape of the coast, in any part of the land, must depend upon a combination of two different causes. The first of these is the composition of the land or solid parts of the coast; if this be uniform and regular, so will be the shape of the coast; if it is irregular and mixed, consisting of parts of very different degrees of hardness and resistance to the wasting operations, the coast will then be, cet. par. irregular and indented. The second, again, respects the wearing power. If this wearing power shall be supposed to be equally applied to all the coast; and, if every part of that coast were of an equal quality or resisting power, no explanation could be given, from the present state of things, for the particular shape of that coast, which ought then to be wasted in an equable manner by the sea. But neither is the coast, of any extensive country at least, composed of such uniform materials; nor is the application of the wearing power to the coast an equal thing; and this will form the subject of another observation. The third general observation, therefore, regards the operations of the sea upon the coast, and the effects which may be perceived in consequence of that cause, independent of the qualities of the coast, or supposing them in general to be alike. Here, according to the theory, we should expect to find deep water and an indented coast upon a country, in proportion as that coast is exposed to the violence of the sea, or is open directly to the ocean. We have but to look along the west coast of Norway, the north-west of Scotland, the west of Ireland, and the south-west of England and of France; and we shall soon be convinced that the sea has made ravages upon those coasts in proportion to its power, and has left them in a shape corresponding to the composition of the land, in destroying the softer, and leaving the harder parts 14.
With those hard and rugged coasts of Britain and Ireland, let us contrast the east coasts; What a difference between these and the west side! Upon the west side, there are no sand banks left upon the coast; the mariner has nothing there to fear but rocks. It is otherwise on the east; here we find a tamer coast, and, in many places, a sandy bottom. On the west, nothing appears opposed to the storm of the ocean except the hardest and most solid rock; on the east, we find coasts exposed to the sea which could not have remained in a similar situation on the west. Let us but compare the two opposite coasts of England, viz. the promontory of Norfolk and Suffolk upon the one side, and Pembrokeshire and Carnarvonshire on the other, both similarly exposed, the one to the north east storm of the German sea, the other to the south west billows of the Atlantic. What a striking difference! The coast in the bay of Cardigan is a hard and strong coast compared with that of Norfolk and Suffolk; the one is strong schistus, the other the most tender clay; yet the soft coast stands protuberant to the sea, the harder coast is hollowed out into a bay; the one has no protection but the sands with which it is surrounded, the other had not remained till this day but for the protection of the most solid rocks of Pembrokeshire and Carnarvonshire, which oppose the fury of the waves.
The last general observation which I shall propose, has, for its subject, a more enlarged view than those now taken of the coast, a view indeed which is not so immediately the object of our observation, but which is nevertheless to be made most evident, by means of the others now considered. We have seen that the land exposed to the sea is destroyed, and the coast wasted more or less, in proportion to the wearing causes, and to the different resisting powers opposed to those causes of decay; we are now to make our observations with regard to the extent and quality of that which has been already destroyed, a subject which can only be conjectured at from the scientific view which may be taken of things, and from the careful examination of that which has been left behind upon the different coasts.
Our land is wasted by the sea; and there is also a natural progress to be observed which necessarily takes place on this occasion; for, the coast is found variously indented, that is to say, more or less, according as the land is exposed to this wasting and wearing operation of the sea, and according as the wasted land is composed of parts resisting with different degrees of power the destroying cause. The land, thus being worn and wasted away, forms here and there peninsulas, which are the more durable portions of that which had been destroyed around; and these remaining portions are still connected with the main land, of which they at present form a part.
But those promontories and peninsulas are gradually detached from the main land, in thus forming islands, which are but little removed from the land. An example of this we have in Anglesay, which is but one degree removed from the state of being a promontory. These islands again, in being subdivided, are converted into barren rocks, which point out to us the course in which the lost or wasted land upon the coast had formerly existed.
To be satisfied of this, let us but look upon the western coast of Scotland; from the islands of St. Kilda to Galloway, on the one side, and to Shetland on the other; in this tract, we have every testimony, for the truth of the doctrine, that is consistent with the nature of the subject. The progress of things is too slow to admit of any evidence drawn immediately from observation; but every other proof is at hand; every appearance corresponds with the theory; and of every step in the progress, from a continent of high land to the point of a rock sunk below the surface of the sea, abundant examples may be found. We do not see the beginning and ending of any one island or piece of country, because the operation is only accomplished in the course of time, and the experience of man is only in the present moment. But man has science and reason, in order to understand what has already been from what appears; and we have but to open our eyes to see all the stages of the operation although not in one individual object. Now, where the nature of things will not admit of having all and every step of the progress to be perceived in one object, an indefinite progression in the various states of different objects, showing the series or gradation from a continent to a rock, must form a proof in which no deficiency will be found.
I have given for example the coast of Scotland; but all over the world where there is a coast not covered with sand, or where it is exposed to the violence of the sea, it is the same. Take the map of any country, provided it be sufficiently particular, and you will see the breaking of continents or islands, first, into promontories or peninsulas; secondly, into islands which stand on the same solid basis with the continent; and, lastly, into rocks which are related to the islands, in like manner as those parasitical islands are related to the head lands and the shore. Here is a general fact, from the simple inspection of which we must conclude one of two things; either that those rocks and smaller islands, which we have termed parasitical, are in a state of progression, by which in time they will be joined to the main land, and form one continent; or that they are in a state of degradation, by which in time they will be made to disappear. There is no other supposition to be made; and, of that alternative, there is no room to hesitate a moment which to choose. This is not a matter of mere probability, it is the subject of physical demonstration. Should we find an old manuscript in a similar condition, we could not conclude with more certainty, that the deficient or intervening places had been destroyed, than we here conclude that the part which is now wanting, between the two remaining portions of the same rock or strata, had once connected those two portions, and had been destroyed by the operation of those causes which are every day employed in still increasing the breach.
Though over all the world, where the shore is washed bare by the sea, examples are to be found which require but to be seen to give compleat conviction, it is not in every place that the eye of a naturalist has been employed in taking this view of the coast; nor is it upon every occasion that enlightened philosophers of this kind have given their thoughts upon the subject. M. de Spallanzani has given us the following observations with regard to the coast of Italy 15.
«Autant l'intérieur du petit bourg de Porto-venere et les rochers qui l'environnent sont a l'abri des tempêtes, autant les parties extérieures sont exposées aux coups de mer les plus violens, lorsqu'elles sont en proie au deux terribles vents d'Afrique et à celui du sud-est. Ce dernier en particulier soulève les flots avec tant de violence et à une telle hauteur contre les écueils qui servent de défense à ce petit terrain, que la mer semble menacer de l'engloutir. J'ai été le témoin d'un de ces orages, et quoique je fusse à l'abri de tout danger, je ne pourroit vous representer l'horreur que me fit éprouver ce spectacle. J'ai voulu prendre avec exactitude la hauteur moyenne de l'élevation des flots dans les plus violens coups de vent; et quand je vous en parlerai vous serez étonné de leur force et de l'étendue de leurs effets. Les rochers qui sont à la partie méridionale de Porto-venere se rongent et se détruisent peu-à-peu de même que les trois isles voisines Tiro, le petit Tiro, et Palmarin. On le remarque surtout dans cette dernier: les bords voisins de la terre ont une pente douce; ils sont couverts d'arbres et de plantes, tandis que la partie opposée est déserte et inaccessible couverte de précipices, de ruines et d'horreurs; les autres parties du rivage sont renfermées par la rivière du ponent et par celle du levant, de même que celles qui s'approchent des côtes de Provence. Il me paroît que la mer a beaucoup gagné sur le terre dans ces parages; et pour parler seulement de Palmarin, la plus grande, et la plus remarquable des trois îsles que j'ai nommées, je crois être suffisamment fondé pour conclure que la même pente facile et longue qu'on observe du côte de la terre avoit aussi existé du côte de la mer; mais que cette dernière avoit été détruite par les orages, qui se sont succédés pendant le cours de siècles. La vue réfléchie de ces trois îsles me force à les regarder comme ayant été autre fois réunies, et formant une îsle seule par leur réunion, ou plutôt comme une presqu'île attenante à Porto-Venere.»
We have a still more interesting observation made upon this same coast of Italy, by a naturalist to whom the world is much indebted for his excellent remarks upon what he has, by his great industry, brought to light. I mean the Chevalier de Dolomieu; where-ever he goes, natural history reaps the benefit of the most enlightened observations. We are now to avail ourselves of his Mémoire sur les Iles Ponces.
The pumice islands form part of a chain of land that may be traced forming a circular line from the cape Missene to the mount Circello at the other side of the Gulf of Gaeta. The islands of Ischia and Procida, which form part of this chain of land, might, from the inspection of the map, be allowed as having once formed a continuation of the land from the continent of Italy, even without the testimony of natural history, that traces this connection from the materials of those masses which now are separated.
The pumice islands form the middle part of that chain, and are the farthest removed from that continent of which it is probable they once formed a part. They are connected with the promontory of Missene on the one hand, as being of the same or similar volcanic origin, and on the other with mount Circello, by a curious circumstance in the island Zanone, which, but a little more of the devouring operation of the sea, would have concealed from our observation.
The island of Ventotiene, which is the nearest of them to Ischia, would appear to be the ancient island of Pendataria, in which Julia was confined. The marks of degradation in this island, I would wish to give in the Chevalier's own words, (p. 52.)
«Cette îsle continue à être devorée par la mer, elle l'attaque dans toutes les parties de son contour, où elle trouve peu de resistance, et elle ne cesse de creuser, principalement, tous les escarpemens du nord. Il paroît, par les vestiges des antiquités qui sont sur la pointe dite di Nevola, que sous l'Empire de César cette îsle avoit encore une étendue plus considérable. Il s'y fait journellement des éboulemens; on peut prévoir qu'elle diminuera progressivement, qu'elle se divisera, et que dans les temps à venir elle sera réduite aux rochers de laves qui la supportent, et qui seuls peuvent résister, pendant une longue suite de siècles, à tous les efforts des flots; ce ne sera sûrement pas la seule terre que le temps et la mer auront dévorée, et que les vicissitudes de la nature ont fait disparoître avant que l'histoire en ait pu constater l'existence.»
As the island of Ventotiene connects this group of the pumice islands with the continent of Missene, that of Zanone, on the other side, connects them with the continent at mount Circello. Here is a fact of which our author now gives proper evidence.
It would appear that Mount Circello is composed of an alpine limestone. But in the north end of the island of Zanone, the Chevalier de Dolomieu finds a small part of a similar limestone in vertical strata, closely united with the volcanic materials of the islands now under consideration. It is impossible that this portion of calcareous rock could be formed in its present situation, and we have but to examine nature in order to be convinced that this limestone part had been once continued from Mount Circello. Here again I beg leave to give this author's own words, (page 141.)
«Cette réunion de deux matières aussi différentes par leur origine que le font celles qui forment l'Isle Zanone, est une circonstance des plus singuliers. La pierre calcaire ne contient point de coquillages; sa densité sa dureté; son odeur fétide annonce une origine ancienne; elle n'est point formée par un dépôt de nouvelle date; elle diffère des pierres calcaires-coquillière qui recouvrent les volcans du Padouan et du Vicentin, et de celles qui se sont mêlés avec les produits du feu dans les volcans éteintes de la Sicile: les laves ici reposent sur elle: elle paroît donc antérieure à l'époque des irruptions qui ont élevé les îsles ponces. Par sa nature elle est semblable aux pierres du Mont Circé, et à celles de l'intérieure de l'Apennin; il semble que cette portion de montagne calcaire, abstraction faite des matières volcaniques qui lui sont réunies, a appartenu à quelqu'unes des montagnes qui dépendent de la chaine qui traverse l'Italie; car il n'est pas possible que ni elle ni le Mont Circé ayent été formés seules et isolés ainsi que nous les voyons. Mais quand ont-ils été détachées? étoient-ils déjà isolés lorsque les feux ont commencé la formation des îsles ponces? ou seroit-ce la même révolution qui les auroit séparés du continent, et qui a opéré le désordre que nous voyons dans ces îsles volcanique? On ne peut former sur toutes ces questions que des conjectures bien vagues.»
Our present inquiry is only with regard to the operation of those causes which we now perceive to be acting upon the coasts of the land; which must be considered as having been operating for a long time back, and which must be considered as continuing to operate. One example more I wish to give, not only as it is much to the purpose, and properly described, but because it contains the natural history of a coast well known from the circumstance of the Giant's Causeway which it contains; a coast composed of stratified chalk indurated and consolidated to a species of marble or lime-stone, and of great masses of basaltes or columnar whin-stone. Now, though our present object is not the formation of land, yet, knowing the mineral constitution of this land, the coast of which we are considering as having been worn by the action of the sea, the view here to be given, of the white marble and basaltic cliffs, is satisfactory in the highest degree. It is from Letters concerning the Northern Coast of the County of Antrim, by the Reverend William Hamilton, A. M.
«The chalky cliffs of the island of Raghery, crowned by a venerable covering of brown rock, form a very beautiful and picturesque appearance as one sails towards them; and, if the turbulence of the sea does not restrain the eyes and fancy from expatiating around, such a striking similitude appears between this and the opposite coast, as readily suggests an idea that the island might once have formed a part of the adjoining country, from whence it has been disunited by some violent shock of nature.
«You, to whom demonstration is familiar, will wonder to see two shores, seven or eight miles asunder, so expeditiously connected by such a slender and fanciful middle term as apparent similitude; and yet the likeness is so strong, and attended with such peculiar circumstances, that I do not entirely despair of prevailing even on you to acknowledge my opinion as a probable one.
«It does not appear unreasonable to conclude, that, if two pieces of land, separated from each other by a chasm, be composed of the same kind of materials, similarly arranged, at equal elevations, these different lands might have been originally connected, and the chasm be only accidental. For, let us conceive the materials to be deposited by any of the elements of fire, air, earth, or water, or by any cause whatever, and it is not likely that this cause (otherwise general) should in all its operations regularly stop short at the chasm.
«The materials of which the island of Raghery is composed are accurately the same as those of the opposite shore; and the arrangement answers so closely, as almost to demonstrate, at first view, their former union. But to explain this more clearly, it will be necessary to give you a general sketch of this whole line of coast.
«The northern coast of Antrim seems to have been originally a compact body of lime-stone rock, considerably higher than the present level of the sea; over which, at some later period, extensive bodies of vitrifiable stone have been superinduced in a state of softness. The original calcareous stratum appears to be much deranged and interrupted by those incumbent masses. In some places it is depressed greatly below its ancient level; shortly after it is borne down to the water's edge, and can be traced under its surface. By and by it dips entirely, and seems irretrievably lost under the superior mass. In a short space, however, it begins to emerge, and, after a similar variation, recovers its original height.
«In this manner, and with such repeated vicissitudes of elevation and depression, it pursues a course of forty miles along the coast from Lough Foyle to Lough Larne.
«It naturally becomes an object of curiosity to inquire what the substance is from which the lime-stone seems thus to have shrunk, burying itself (as it were in terror) under the covering of the ocean: And, on examination, it appears to be the columnar basaltes, under which the lime-stone stratum is never found; nor indeed does it ever approach near to it without evident signs of derangement.
«Thus, for example, the chalky cliffs may be discovered a little eastward from Portrush; after a short course, they are suddenly depressed to the water's edge, under Dunluce Castle, and, soon after, lost entirely in passing near the basalt-hill of Dunluce, whose craigs, near the sea, are all columnar. At the river Bush the lime-stone recovers, and skims a moment above the level of the sea, but immediately vanishes in approaching towards the great basalt promontory of Bengore, under which it is completely lost for the space of more than three miles.
«Eastward from thence, beyond Dunsaverock Castle, it again emerges, and, rising to a considerable height, forms a beautiful barrier to White Park Bay and the Ballintoy shore. After this it suffers a temporary depression near the basalt hill of Knocksoghy, and then ranges along the coast as far as Ballycastle Bay.
«Fairhead, standing with magnificence on its massy columns of basaltes, again exterminates it; and once again it rises to the eastward, and pursues its devious course, forming, on the Glenarm shores, a line of coast the most fantastically beautiful that can be imagined.
«If this, tedious expedition have not entirely worn out your patience, let us now take a view of the coast of Ragery itself, from the lofty summit of Fairhead, which overlook it. Westward we see its white cliff rising abruptly from the ocean, corresponding accurately in materials and elevation with those of the opposite shore, and like them, crowned with a venerable load of the same vitrifiable rock. Eastward, we behold it dip to the level of the sea, and soon give place to many beautiful arrangements of basalt pillars which form the eastern end of the island, and lie opposite to the basaltes of Fairhead, affording in every part a reasonable presumption that the two coasts were formerly connected, and that each was created and deranged by the same causes extensively operating over both.
«But it is not in these larger features alone that the similitude may be traced; the more minute and accidental circumstances serve equally well to ascertain it.
«Thus, an heterogeneous mass of freestone, coals, iron-ore, etc. which forms the east side of Ballycastle Bay, and appears quite different from the common fossils of the country, may be traced also directly opposite, running under Rathlin, with circumstances which almost demonstrably ascertain it to be the same vein.
«What I would infer from hence is, that this whole coast has undergone considerable changes; that those abrupt promontories, which now run wildly into the ocean, in proud defiance of its boisterous waves, have been rendered broken and irregular by some violent convulsion of nature; and that the island of Ragery, standing as it were in the midst between this and the Scottish coast, may be the surviving fragment of a large tract of country which, at some period of time, has been buried in the deep.»
Besides this argument of the gradation from a continent of land to a bare rock, we have another from the consideration of those rocks themselves, so far as these could not be formed by nature in their present state, but must have been portions of a greater mass. How, for example, could a perpendicular mountain, such as St. Kilda, have been produced in the ocean? Of whatever materials we shall suppose it formed, we never shall find means for the production of such a mass in its present insulated state. Let us take examples of this kind near our coast, and of known rocks. Staffa and Ailsa, on the west coast, and the Bass, upon the east, are mountains of either whin-stone or granite, similar to many such mountains within the land; and they are perpendicular around, except perhaps on one part. It is demonstrable that such basaltic rock as contains zeolite and calcareous spar, as most of our whin-stones do, could not have been the eruption of a volcano, consequently those rocks must have been masses protruded in a fluid state, under an immense cover of earth at the time of their production; and they could not have risen immediately out of the sea, with all their various minerals, their veins and cutters, their faces and their angles.
In like manner, the east coast of Caithness is a perpendicular cliff of sand-stone, lying in a horizontal position, and thus forming a flat country above the shore. But along this coast there are small islands, pillars, and peninsulas, of the same strata, corresponding perfectly with that which forms the greater mass. Now, shall we suppose those strata of sand-stone to have been formed in their place, and to have reached no farther eastward into the sea?—It is unsupposable. Or, shall we conceive that the sea, which has made such depredations in land composed of much more solid materials, had spared this, and had not wasted much more than that now pointed out by the ruins which remain?—Impossible; we must suppose that there had once existed much land where nothing now is found but sea. But, if we are to suppose much to have been wasted, where shall we stop in this process of restoring continents? That is the question now to be discussed.
With this view, let us now turn our attention to the north-west coast of Europe, in consulting the general as well as the most particular maps. Upon the one extremity of Britain, we find Cornwall separating it as it were from the main land; and, from this promontory, the Scilly Isles pointing out what had been destroyed in that direction, which is here to be considered as the line of greatest resistance. But what a quantity of the soft materials, or less resisting parts on either side, has been destroyed! Upon the other extremity of Britain, we find the country of Scotland, forming itself into promontories and islands, and those islands and rocks pointing out to us what had been the former extent of our continent and land around. But, in following this connection of things, we cannot refuse to acknowledge that Ireland had formerly been in one mass of land with Britain, in like manner as the Orkneys had been with Scotland 16.
It will be still less possible to refuse the junction of England with the continent of France; the testimony of that peculiar body of chalk and flint, which borders each of those opposite coasts, forms an argument which is irrefragable. Now, in order to complete our continent, we have only to connect the Shetland islands with the coast of Norway. But this is a notion which, however probable it may appear, is not proposed as a fact immediately supported by natural appearances; it is only to be considered as an enlarged view in which we may contemplate the operations of this earth upon a more extended scale; one which may be conceived as a step in our cosmogeny, and one which, while it illustrates the theory of the earth already given, is by no means required in order to confirm a theory founded upon appearances which leave no manner of doubt.
v2:14 M. de Lamblardie, ingénieur des ponts et chaussées, has made a calculation, seemingly upon good grounds, with regard to the wasting of a part of the coast of France, between the Seine and the Somme. This coast is composed of falaises, (or chalk cliffs, like the opposite coast of England), which are 200 feet high above the level of the sea, composed of strata of marl, separated by beds of flint. This coast is found to be wasted, at an average, at the rate of one foot per annum. We may thus perhaps form some idea of the time since the coast of France and that of England had been here united, or one continued mass of those strata which are the same on both those coasts.
v2:15 Observations sur la Physique, etc. Juillet 1786.
v2:16 I have the most satisfactory evidence of this fact, in finding the schistus of Galloway and of England in the opposite coast of Ireland, corresponding to its direction in stretching from the coasts of Britain.
