GNEISS. 149 



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 ; bat may probably be 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 be 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- 



