SIMMONS — EVIDENCE OE GLACIAL ACTION IN SCOTLAND. 167 
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 EifFelhorn : " 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 Gorner glacier. It was red and 
liard, 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, ^larch 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 6. 
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 . . . IS'S Fe 14'4 
Lime 38 
Magnesia 1-5 
Potash 2-6 
Loss at red heat, water . . 6 2 
99-4 
Crust, or altered stone. 
Insoluble matter .... 72*5 
Peroxide of iron . . . . 19-7 Fe 13-8 
Lime 09 
Magnesia 03 
Potash trace 
Loss at red heat .... 5*1 
99-2 
" Here, then, we find that water has dissolved out lime, iron. 
