1854.] SHARPE STRUCTURE OF MONT BLANC. 19 



on the examination of the wild region to the south of Mont Blanc, 

 we may soon hope to see it properly described. The ascent from 

 the West is principally over dark slates of the anthraxiferous series, 

 which form a very irregular and disturbed anticlinal ; they are tra- 

 versed by cleavage dipping usually E. 25° to 30° S., at angles in- 

 creasing as we ascend the hill from Nant Bourant. These are sur- 

 mounted by a great series of Jurassic beds, in which I noted the 

 following descending series, which, however, was taken down too 

 hastily to be given as more than a rough approximation. 



Hard slate, seen at Chapieux ; cleavage well-marked. 



Slaty limestone ; cleavage distinct. 



Hard quartzose grit, without cleavage. 



Black slate of great thickness, with quartz veins along the planes 

 of cleavage, which are wavy, and somewhat irregular. 



Quartzose grit, without cleavage. 



Grey siliceous limestone, without cleavage. 



Rotten black slate, with marked cleavage ; on which the Second 

 Cross stands. 



Hard grit, free from cleavage. 



Soft black shale. 



Sandstone and calcareous conglomerate alternating with beds of 

 hard blue limestone, the whole free from cleavage. 



Sandstone, with distinct cleavage. 



Hard grit, without cleavage. 



Hard metamorphic grit, with marked cleavage running up to the 

 Bonhomme. 



Hard siliceous limestone, without cleavage, probably the base of 

 the Jurassic series. 



Indurated sandstone passing into quartz rock, with innumerable 

 joints; cleavage obscure ; probably the commencement of the anthraxi- 

 ferous series. 



Hard siliceous limestone, free from cleavage, on which stands the 

 First Cross. 



Hard quartzose grit, without cleavage. 



Black slates. 



The Jurassic beds all dip either S.E. or E.S.E. from 20° to 30°; 

 their cleavage is vertical on the top of the Pass, and dips N. 30° W. at 

 regularly decreasing angles from the top to the Second Cross, where it 

 forms an anticlinal. The strike of the cleavage varies fromN. 25° E. 

 to N. 60° E. 



I should not have offered a section so hastily drawn up, but for 

 the interest attaching to the arrangement of the cleavage planes. In 

 the first place it is to be observed, that many of the hardest beds, 

 best able to resist pressure, are quite free from cleavage ; while other 

 beds, both above and below them, are so thoroughly cleaved as to be 

 quite slaty. And the intercalation of the compact beds has very 

 little altered the direction of the planes of cleavage in the other beds, 

 which are nearly conformable ; though perhaps rather less regularly so 

 than appears in my section. I observed a similar alternation of slaty 

 and compact beds, in many other parts of the Alps, in the uppermost 



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