PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 549 
And these were cut by the operation of the very agents which—acting 
during an epoch that may to a certain extent be measured by that of the 
human tenancy of the globe—have failed even to smooth out the minute tracery 
of the ice. 
Trifling as the amount of the action is here, and vast as it has been there, 
that action, and the chief agent in that action, will be found to be the same in 
both cases. Water—water everywhere. 
Arenaceous rocks are disintegrated through the solution of the trifling 
amount of the calcareous and magnesian cement which unites their grains ; 
and which, once soaked out from between these grains, leaves them to the 
brushing of winds or the scouring of waters. Rocks which contain felspar 
assume the appearance of a rasp, from the decay of that felspar, the alkalies 
of which are called for elsewhere, and are borne away on the chariot wheels of 
the raindrop ;—“the highest parts of the dust of the world” may have had 
nobler uses assigned to it than the mere nurturing of lichens. 
Carrying with us to Harris the lesson learned in the schoolroom of Suther- 
land, and holding our course along the ridge of the Red Scuir, we note the 
geognostic facts that its eminences gradually diminish in height and in width as 
we proceed westward; and that they are accompanied, for about the first half of 
the six or seven miles of their length, by a series of lakes, also gradually diminish- 
ing in size. As these lakes maintain a constant distance from the serpentinous 
ridge, and underlie it in position, they have the greatest possible resemblance 
to a washed-out lime stratum. 
As a lithological fact, again, it is to be noted that while at the more easterly, 
the loftier end of the red ridge, the whole rock is a massive perfectly-formed 
serpentine ; as we approach the west, foliaceous flakes of enstatite, or some 
one of the minerals which cluster round augite, become visible. Further west 
still, where the ridge begins to diminish in height, and the lakes are represented 
merely by swampy ground, the hornblendic type of mineral appears as a matted 
—$——— TE 
asbestiform actynolite ;* while at its termination, in the comparatively low Dun 
of Borve, true unaltered hornblende of the smaragdite type is alone seen,— 
mixed, however, with a concreting felspar. 
Southward of, that is beneath this, there is no appearance of swamp, or any 
evidence direct or indirect of the presence of lime. 
The condition of things when the outcrops of the system of rocks was first 
exposed to the operation of the agents of change would therefore appear to 
haye been this ;—there were to the north, beds of the ordinary hornblendic gneiss, 
succeeded, in descending order, by a bed of rock which was hornblendic to the 
* Jameson says that he found enough of this in the island to load an Indiaman,—and this is the 
spot where it occurs. 
VOL, XXVIII. PART II. 7c 
