SIMMOTsS EVIDENCE OF GLACIAL ACTION IN SCOTLAND. 1G7 



observed on trap, or rather the species of trap termed basalt. In the 

 143rd page of his - Glaciers of the Alps,' he says, in describing the 

 lower spur of the Riffelhorn : " Midway down the spur I lighted 

 upon a transverse wall of rock, which formed in earlier ages the 

 boundary of a lateral outlet of the Grorner glacier. It was red and 

 hard, weathered rough at some places, and polished smooth at others. 

 The lines were drawn finely upon it, but its outer surface appeared 

 to be peeling off like a crust ; the polished layer rested upon the 

 rock like a kind of enamel. The action of the glacier appeared to 

 resemble that of the break of a locomotive upon rails ; both being 

 cases of exfoliation brought about by pressure and friction." This 

 crust is observed on basalt boulders taken out of semicircular mounds, 

 probably caused by glacial action ; portions of the crust can easily be 

 removed. My illustrious and valued friend Mr. James Napier, 

 F.C.S., in his valuable " Eemarks on Mineral Veins and Waterworn 

 Stones," read before, and published in the Transactions of the 

 Philosophical Society of Glasgow, March 3rd, 1852, has proved, 

 beyond doubt, that this crust is not the result of pressure but of 

 water. This eminent chemist maintains that water, in contact with 

 and passing through rocks, changes their character, by dissolving out 

 some of their component minerals. The following extract, although 

 long, I cannot refrain from giving, as it clearly explains how the 

 remarkable crust found to exist on trap or basalt rocks originates : — 

 "A piece of trap rock, e.g., exposed to water, very soon changes, 

 when alternately wet and dry, and exposed to the atmosphere ; the 

 decomposition is sensibly apparent, a brown crust is soon formed, 

 which becomes soft and brittle, breaking off by slight friction, leaving 

 a new portion of the stone to undergo the same change. The same 

 sort of stone embedded in the gravel under the soil, passes through 

 the same changes, but the crust in this case is not so soft and 

 brittle ; the change soon penetrates to the centre of the stone, giving 

 it a different character and appearance." I lately removed portions 

 of the crust from such boulders, taken from a railway cutting in this 

 neighbourhood, almost half an inch thick, and about 12 inches by G. 

 Much larger fragments could easily be obtained. " Analysis," con- 

 tinues Mr. Napier, " of the stone so changed, compared with the 

 original, makes the change very apparent. We give the average of 

 many analyses from different localities : — 



Kernel, or original stone. 



Insoluble silicate of alumina 66*8 



Protoxide of iron . . . 18 5 Fe 14r4 



Lime 3 "8 



Magnesia 1/5 



Potash 2-6 



Loss at red heat, water . . G'2 



99-4 



Crust, or altered stone. 



Insoluble matter . . . . 7~'5 



Peroxide of iron .... 19'7 Vc 1 3'S 



Lime 09 



Magnesia 03 



Potash trace 



Loss at red heat . . . . .VI 



992 



"Here, then, we find that water has dissolved out lime, iron, 



