Ch.XXVL] , 



IN CONTACT WITH GRANITE. 



371 



near the contact with the veins. These appearances are well 

 seen at the junction of the granite and killas in St. Michael's 

 Mount, a small island nearly 300 feet high, situated in the bay, 

 at the distance of about three miles from Penzance. 



In the department of the Hautes Alpes, in France, near 

 Vizille, M. Elie de Beaumont traced a black argillaceous 

 limestone, charged with belemnites to within a few yards of a 

 mass of granite. Here the limestone begins to put on a 



No. 90. 



Junction of granite ivith Jurassic or oolite strata in the Alps, near Champoleon. 



granular texture, but is extremely fine-grained. When nearer 

 the junction it becomes grey and has a saccharoid structure. 

 In another locality, near Champoleon, a granite composed of 

 quartz, black mica, and rose-coloured felspar, is observed 

 partly to overlie the secondary rocks, producing an alteration 

 which extends for about thirty feet downwards, diminishing in 

 the inferior beds which lie farthest from the granite. (See wood- 

 cut No. 90.) In the altered mass the argillaceous beds are 

 hardened, the limestone is saccharoid, the grits quartzose, and in 

 the midst of them is a thin layer of an imperfect granite. It is 

 also an important circumstance, that near the point of contact 

 both the granite and the secondary rocks become metalliferous, 

 and contain nests and small veins of blende, galena, iron, and 

 copper pyrites. The stratified rocks become harder and more 



2 B 2 



