GEOLOGICAL OBSEBVATIONS IN FRANCE. 



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other toward the valley of Villy, which is parallel with this. 

 Its ascent tVom the priory, though steep, is practicable to 

 ubout two thirds of its height, through fragments of lamel- ^ 



lur rocks, mixed with quartz, feldtspar, and mica, in every 

 possible proportion, and of different degrees of hardness, 

 from the hardest lamellar granite to the softek micaceoo* 

 rock. These fragments come either from the summit or 

 from the flanks of the mountain. The summit in particular 

 is formed of a rock, that appears to belong to the class of 

 true granites, notwithstanding the parallel situation aHected 

 by the scales of mica, that form part of it. The back of 

 the mountaiu is composed in great measure of a veined gra- 

 nite, tvith lenticular crystals of quartz of various sizes, but 



*ttoging in the direction of the laminae. 



?■ The Aiguilles, or needles, on the south-east of the ralley Needles. 

 bf Chamouni, are five lofiy ])yramid9, decreasing in height 

 from the southernmost to the northernmost. The base that 

 supports them, which rises seven or eight hundred toi^ea 

 above the valley, is composed of lamellar rocks of different 

 kinds, but chietly quartzose or micaceous, arranged in very ? 



regular strata, and running in the direction of the valley. 

 Their inclination toward the bottom of the mountains is 

 very little, but they gradually rise against the valley to the 

 top, where they are exactly vertical. The higher up the, 

 mountain they are, the more they approach the nature of 

 gtanite. The pyramids that rise above this are of granite 

 in mass. They are composed externally of pyramidal la- 

 rninse, subdivided into strata parallel to the planes of the 

 larainse themselves. These laminae are nearly vertical, and 

 do not lean against the valley, like the lower strata of the 

 inountain, but agninst the body of the pyramid. The heart 

 of the pyramids, or their interior part, appears in some places 

 to have no regular structure, and to be divided only by ac- 

 cidental clefts. These pyramids however must not be ima- 

 gined to stand upon the mass below, as a pillar on its bai?e : 

 on the contrary they must have a base of their own beneath, 

 on which the strata of this mass in part reist. . C 



The Aiguille du Dru is of a nearly similar structure, but Aiguille da 

 among the fragments at its foot are blocks of primitive pe- ^^^' 

 trosilex, with a great deal of feldstpar, and a little mica. 



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