92 Prof. Forbes on the Topography arid Geology of the 



ents does not influence this general tendency to evenness of 

 surface. The felspar and the hypersthene'of the hypersthene 

 rock are equally flat, only where the rock has been much ex- 

 posed, the surfaces of the hypersthene concretions are in a 

 plane just so far relieved from the felspar of the composi- 

 tion as to give the rasping roughness so characteristic of the 

 hypersthene rock, wherever it has been long exposed to the 

 weather. 



5. But the most remarkable circumstance is, that when 

 the hypersthene rock is traversed by clay stone veins, which 

 it is constantly, or by veins of crystallized hypersthene and 

 magnetic iron, these various parts of such diff*erent hardness 

 are all uniformly shaven over, in conformity with the general 

 form of the mass to which they belong. This presents a 

 striking analogy to the phenomena of polished rocks in the 

 Alps, where the quartz veins are cut off parallel to the sur- 

 face of the bounding felspar. 



6. The surfaces of hypersthene, ihu^ planed or evened, pre- 

 sent systems of grooves exactly similar to those so much in- 

 sisted on in the action of glaciers on subjacent rocks, and 

 as evidence of the existence of glaciers in parts of the Alps 

 and Jura where they are now awanting. These grooves or 

 striae ^re as well marked, as continuous, and as strictly 

 parallel, to what I have elswhere shewn to be the necessary 

 course of a tenacious mass of ice urged by gravity down a 

 valley, as anywhere in the Alps. They occur on high verti- 

 cal cliffs, as near the Pissevache ; they rise against opposing 

 promontories, as in the valley of Hasli ; they make deep chan- 

 nels or flutings in the trough of the valley, as at Pont Pe- 

 lissier, near Chamouni, and as at Fee in the valley of Saas. 

 At the same, these appearances have a superior limit, above 

 which the craggy angular forms are almost exclusively seen, 

 and where the phenomena of wearing and grooving entirely 

 disappear. 



7. The occurrence of large angular detached masses of 

 hypersthene poised upon others, or fantastically balanced on 

 the insulated tops of the elliptical domes of rock. 



In short, it would be quite impossible to find in the Alps, 

 or elsewhere, these phenomena (excepting only the high 



