136 



The Glacial Theory. 



For the manner in which such poHshings and grooves are 

 efFected by glaciers, we may refer to p. 449, of the Calcutta 

 Journal of Natural History ^ 184^. Dr. Buckland, to whom 

 these polished surfaces were pointed out in Switzerland by 

 Professor Agassiz, as the effect of glaciers, remarked, that 

 he had seen similar phenomena on the surfaces of rocks 

 both in Scotland and England, but which he had attributed 

 to diluvial action. Thus he had observed on the head rocks, 

 on the left side of the gorge of the Tay near Dunkeld, round- 

 ed and polished surfaces; and in 1824, in company with Mr. 

 Lyell, grooves and strias on granite rocks near the east base 

 of Ben Nevis. About the same time, Sir G. Mackenzie 

 pointed out to Dr. Buckland a high ridge of gravel extended 

 across a valley at the base of Ben Nevis, in a manner 

 inexplicable by any action of water ; but in which, from his 

 examination of glaciers in Switzerland, he recognizes the 

 form and condition of a moraine. The north and north-east 

 shoulders of Schihallien presents rounded, polished and 

 striated surfaces. Again, on the left flank of the valley call- 

 ed the Braes of Foss, a newly exposed porphyry of the 

 dyke, forty feet wide, exhibited a polished and striated sur- 

 face parallel to the line of descent which a glacier from 

 Schihallien would take, and in the right flank of the same 

 valley, another and smaller dyke of porphyry presented simi- 

 lar phenomena, and in the intermediate space, the recently 

 uncovered slate and quartzose rock, are rounded, polished, 

 grooved, and striated parallel in the direction, which a glacier 

 would assume. At the west end of Comrie near Strath Earn, 

 blue slate rocks have been also rounded and guttered, as 

 well as the surface of the granite at Invergeldy ; though too 

 much weathered, the polished surface or the striae, both of 

 which phenomena may, however, be seen on a hill composed 

 of trap rock near Surg, in the direction which a glacier des- 

 cending the subjacent valley would assume. 



2. Moraines, — Dr. Buckland on the same occasion enters 

 into full particulars of moraines or ridges of loose boulders, 



