162 Charles Maclaren, Esq., on Grooved and Striated Rocks 



sea, westward or southward, producing groovings on the 

 rocks, and the phenomena of crag-and-tail, in directions cor- 

 responding to tlie course of the i*eturn waves. 



This theory bears the stamp of the acute and original 

 mind of its author, and it offered perhaps the best explana- 

 tion of the phenomena, whicli tlie range of geological infor- 

 mation at that time could supply. In the same year we find 

 specimens of striated rocks and crag-and-tail noticed by 

 Colonel Imrie, in his paper on the Campsie Hills, in the se- 

 cond volume of the Wernerian Society's Transactions, and 

 an idea somewhat similar as to their origin thrown out. Sir 

 James Hall's explanation of the phenomena was pretty ge- 

 nerally accepted by geologists in this country ; and it is still, 

 I believe, adopted, though perhaps in a modified form, by 

 some able men. I shall notice very biMefly a few of the lead- 

 ing objections to it. 



\st. Striae must have been produced by a sliding motion, 

 like that of a plane or graving tool, while stones propelled 

 over a firm surface, by a current of water, would have a roll- 

 ing motion, which might polish the rocks, but could not cut 

 groves in them. 2d, Supposing stones impelled by water to 

 cut grooves, these grooves would not occupy such positions 

 as we find them in, on sloping surfaces like the steep sides 

 of valleys ; the force of gravity would render them more or 

 less inclined, while, in such situations, we find them horizon- 

 tal. 3fl^, The groovings so cut would be deflected to the 

 right or left, by slight inequalities of surface, and would not 

 possess that wonderful straightness and parallelism which 

 they generally exhibit, and which Mr Lyell has seen extend- 

 ing over a length of 100 yards in the United States. Ath, A 

 great wave or debacle of the magnitude assumed, coming 

 from the west or north-west, would have filled up deep val- 

 leys transverse to its course, like that called the Great Glen. 

 Now, that glen, so far from being filled up, has a depth of 

 770 feet in Loch Ness, measured from the surface of the 

 water, — a depth exceeding that of the German Ocean. The 

 fact, that this deep fissure has not been filled up, is presump- 

 tive evidence, that no such wave has ever passed over the 



