675 
A year and a half only has elapsed since Professor Agassiz and 
Dr. Buckland seemed to think, that this district was as rich in 
proofs of the action of glaciers as many other parts of Scotland 
which they visited, and as I happened to witness the efforts of my 
predecessor in this Chair to attach Mr. Maclaren to his views, I 
must be permitted to direct your attention to the practical results 
at which this gentleman has arrived, in some prominent cases. 
Observing blocks of greenstone on Arthur's Seat, which, from 
their peculiar structure, must have been transported from Salisbury 
Craigs, a lower hill, and separated from the former by an abrupt val- 
ley, Mr. Maclaren infers, that if the present surface of the land be 
argued upon (and in all questions of glaciers this is a postulate), nei- 
ther glacier, nor iceberg, nor current will explain the fact. It is un- 
necessary that I should here examine this author's hypothesis, by 
which in order to solve the local problem, he restores the inclined 
stratified masses of Salisbury Craigs to such an extent as to give 
them an altitude in ancient times superior to that of Arthur’s Seat ; 
for whether we adopt his ingenious view, involving a mighty sub- 
sequent denudation, or suppose that in the oscillations of this plu- 
tonie tract the former low and high points of land have been re- 
latively depressed and elevated, it is obvious, from the very strue- 
ture of the rocks, that in both cases a subaqueous, and not a sub- 
aérial condition is called for to explain the appearances, and this 
too, be it recollected, on the summits of the highest hills in the im- 
mediate vicinity of the Scottish metropolis, in and around which 
the action of glaciers has been supposed to be visible at much lower 
levels ! 
Among the examples of the scratched and polished surfaces of 
rocks near Edinburgh, I do not perceive that the glacialists have 
grappled with certain appearances on which Dr. Buckland for- 
merly dwelt with so much pleasure, viz. the grooved or channeled 
surfaces of the Braid Hills, first pointed out by Sir James Hall, 
and which the great chemical geologist attributed to a powerful 
rush of waters. When I visited the low ridge in question with Dr. 
Buckland and other friends*, my conviction was that these grooves, 
though then attributed by Dr. Buckland to glacial action, are due 
neither to that agency, nor to any rush of waters, but are simply 
the result of the changes which the mass of the rock underwent, 
when it passed from its former molten or pasty condition into a 
solid state. These appearances differ essentially from ordinary gla- 
cial scratches or scoringst. ‘They are, in fact, broad undulations 
or furrows, and instead of trending from the higher grounds to 
the Firth ef Forth, as would naturally be the case if they were due 
to the expansion and descent of glaciers, they rise up to the very 
summit of the low ridge in a direction transverse to its bearing, 
and with no neighbouring point of ground higher than that on 
which they occur. On clearing away the thin turf which barely co- 
* Dr. Graham and Mr. Maclaren were of the party, in Oct, 1840. 
+ Plaster casts of these exist in the Geological Society. 
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