128^ Mr Murchison <5?i the Glacial Theory. 



Iiave obstructed the road-ways or passes of our ancestors. Tims is the 

 supposed anomaly explained without recurring to any change of climate."* 



In that part of our own country to which the glacial theory has been 

 applied, Mr Charles Maclaren, already known to you by excellent geolo- 

 gical treatises, has recently published a well-condensed small work ex- 

 plaining the views of Agasslz. The phenomena of glaciers and the general 

 doctrines derived from their study being explained, Mr Maclaren proceeds- 

 to analyze those cases of transported detritus in the neighbourhood of 

 Edinburgh to which tlie theory had been supposed to apply. 



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 at- 

 tention 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 Crags, a 

 /ower hill, and separated from the former by an abrupt valley, Mr Maclaren 

 infers, that if the present surftice of the land be argued upon (and in all 

 questions of glaciers this is a postulate), neither glacier, nor iceberg, nor 

 current will explain the fact. It is unnecessary 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 Crags to such an ex- 

 tent as to give them an altitude in ancient times superior to that of 

 Arthur's Seat; for whether w^e adopt his ingenious view, involving a 

 mighty subsequent denudation, or suppose that in the oscillations of this 

 plutonic tract the former low and high points of land have been relatively 

 depressed and elevated, it is obvious, from the very structure of the rocks, 

 that in both cases a subaqueous, and not a subaerial condition is called 

 for to explain the appearances, and this too, be it recollected, on the sum- 

 mits of the highest hills in the immediate vicinity of the Scottish metro- 

 polis, 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 formerly dwelt with so much 

 pleasure, viz. the grooved or channeled surfaces of the Braid Hills, first 



* I hoped to have been able to quote the opinions of Professor J. Forbes on 

 this vexata qwzitio, because it is well known that he was a companion of Professor 

 Agassiz in the Alps during the last summer, but this distinguished cultivator of 

 physical science has not jet published his views on the action of glaciers as affect- 

 ing the surface of the earth, though he has given to the public a very ingenious 

 sketch, descriptive of a peculiar parallel striation in the solid ice of glaciers, — 

 Edinburgh New Philosophical Journal, January 1842. 



