All the stones in these two great groups are Sarsens, as they are locally called, a peculiar class of silicious sandstone that is found as a local deposit in the bottoms of the valleys between Salisbury and Swindon. It is the same stone as is used at Avebury, the difference being that there the stones are used rough in their natural state, here they are hewn and fitted with very considerable nicety. Each of the uprights has a tenon on its surface, and the undersides of the architrave, or horizontal piece, have each a mortice, or rather two mortices, into which these tenons fit with considerable exactness.
Besides these there are even now eleven stones, some standing, others thrown down, but still existing, within the inner circle. These are of a different nature, being all cut from igneous rocks, such as are not to be found nearer than Cornwall or even Ireland. It has not been exactly ascertained whence they came; indeed, they seem to be of various kinds, and consequently must have been brought from different places. Locally they are called Blue
