In the rear of some of the best-preserved platforms are stones said to have been erected for sacrificial purposes. These altars consist of a single shaft, generally of vesicular lava, but in some cases cut from the material of which the images and crowns were, made. They range in height from 5 to 10 feet, squared to 3½ or 4 feet on each face, and stand in the center of a terrace paved with smooth bowlders. The sides and plinth were covered with figures sculptured in low relief, but are now too much weather-worn to be traced. These altars are said to have