550 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
west and augitic to the east; this, again, by other strata of the gneiss; and 
these, lastly, by the garnetiferous eklogite. 
The action of the graving tools on each variety of rock is, so far, certain. 
The gneissic rock, physically tough, is inherently most prone to degradation ; 
highly felspathic, it yields the alkalies of the felspar to carbonated waters ; the 
residual kaolinic mud is swept away by every raindrop and every stream; and 
the loosened quartz grains are removed from its surface by every gust of wind. | 
Vast tracts of barren sands along the shores of these islands speak unmistak- 
ably to the great waste which the rock has suffered. 
Of the succeeding stratum, one extremity—the augitic—is more subject to 
change perhaps than even the gneiss ; but it is a change which does not result 
in its disintegration and its waste. Considered as an augitic rock, it may be 
said to be most prone to rotting; but it is a process of rotting which enables 
it to endure. As arock mass, it is a transmutation, not a decay. 
The outcome of its primal weakness is its abiding strength. After the 
transmutation, it is no longer subject to the further operation of the agents 
which transmuted it. Into its dense structure the carbonic acid cannot force — 
its way; nor is there aught now there for that carbonic acid to combine with; 
while off its oily surfaces the raindrop flows unabsorbed. It might, not 
altogether inaptly, be termed the adipocere of rocks. 
During all the period of the transmutation of the augitic extremity of the 
ridge, the western, formed of the less alterable hornblendic mineral, is falling 
to pieces from the disintegration of its felspar, and is being swept away as a 
hornblendic sand. 
The last rock of the district, consisting chiefly of garnet—rich in alumina, 
which forms no natural carbonate—almost defies decay ; garnetiferous sands 
being residues almost as enduring as siliceous ones. 
So that, when, after long subjection to the operations of the Spirit of the 
Storm, he thought to put some sort of a polish upon his work, and the ice 
settled down upon the land, it found in the southward a lofty elevated ridge 
of enduring garnet, succeeded to the north by a low and wasted plain, in the 
midst of which there projected, high in air, a rugged ridge with a russet coat. 
Doubtless the gouging ice would soon have made an end of the almost 
pulpy protuberances,—those terrific gashes showed that the scalping-knife was 
making quick work ; but the great ice age came to an end first ; the fiat, “thus 
far,” or “thus long,” had gone forth ; and the Red Rock henceforth shall stand 
erect in the grim wilderness, a type of those things which “out of weakness 
are made strong.” 
Turning our attention next to the modes of occurrence and lithological 
associations of the unaltered varieties of augite and hornblende, the first direc- 

