system, as the Germans have thus intruded their topaz rock and their weissstein into it. This is a com pound of hornblende and garnet; the structure being small spheroidal, and the whole analysis extremely difficult. It occurs in Guernsey and Sark. I must lastly notice the granite which occurs in an apparently regular stratification with gneiss, and which has aided in giving rise to the opinion that granite was a stratified rock. It is sufficiently easy to dis tinguish these beds from conformable veins ; and they are then true portions of the gneiss, as much stratified as the rock in which they are contained. They, occur only in the granitic varieties, and pass by gradation into the surrounding foliated rock. As far as I have observed, they rarely exceed a few feet in thickness, often not many inches ; but may probably he found of much greater dimensions. Even then, they would not prove the stratification of granite, which possesses characters not to be mistaken; while, on considering the near approach to a purely granitic stratum which gneiss so often undergoes, it can excite no surprise to find the foliated disposition occasionally disappear. The association of gneiss with other independent rocks, in the order of precedence or succession, forms that part of its geological history which, from the pre valence of an erroneous theory, is most in need of illus tration. It has been said to follow necessarily in order after granite ; but it will he seen that it succeeds al most every one of the primary rocks, and may conse quently be followed by any one of the series, and even by the secondary strata. If, in many parts of Scotland, it does occur in this manner, it is not, in those places, the sole rock which immediately follows that one ; so that the correlative rule, which would exclude every other stratum from that position, is false, as has been shown in the last chapter. Its alternations with mi-