724: 



PLUTONIC KOCKS OF THE 



[Ch. XXXIV, 



Fig. 751. 



Period of Oolite and Lias. — In the Department of the Hautes 

 Alpes, in France, 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 granular texture, 

 but is extremely fine-grained. When nearer the junction it becomes 

 gray, and has a saccharoid structure. In another locality, near Cham- 

 poleon, a granite composed of quartz, black mica, and rose-colored 

 felspar is observed partly to overlie the secondary rocks, producing 



an alteration which extends 

 for about 30 feet down- 

 wards, diminishing in the 

 beds which lie farthest from 

 the granite. (See fig. 751.) 

 In the altered mass the 

 argillaceous beds are hard- 

 ened, the limestone is sac- 

 charoid, the grits quartzose, 

 and in the midst of them 

 is a thin layer of an im- 

 perfect granite. It is also 

 an important circumstance, 

 that near the point of con- 

 tact, both the granite and 

 the secondary rocks be- 

 come metalliferous, and 

 contain nests and small 

 veins of blende, galena, 

 iron, and copper pyrites. The stratified rocks become harder and 

 more crystalline, but the granite, on the contrary, softer and less per- 

 fectly crystallized near the junction.'* 



Although the granite is incumbent in the above section (fig. 751), 

 we cannot assume that it overflowed the strata, for the disturbances 

 of the rocks are so great in this part of the Alps that their original 

 position is often inverted. 



A considerable mass of syenite, in the Isle of Skye, is described by 

 Dr. MacCulloch as intersecting limestone and shale, which are of the 

 age of the lias.f The limestone, which at a greater distance from the 

 granite contains shells, exhibits no traces of them near its junction, where 

 it has been converted into a pure crystalline marble.J 



At Predazzo, in the Tyrol, secondary strata, some of which are 

 limestones of the Oolitic period, have been traversed and altered by 

 plutonic rocks, one portion of which is an augitic porphyry, which 



Junction of granite with Jurassic or Oolite strata in 

 the Alps, near Champoleon. 



* Elie de Beaumont, sur les Montagnes de l'Oisans, &c. Mem. de la Soc. d'Hist 

 Nat. de Paris, torn. v. 



f Murchison, Geol. Trans., Second Series, vol. ii. part ii. pp. 311-321. 

 % Western Islands, vol. i. p. 330, plate 18, figs. 3, 4. 



