GEOLOGY. 



\L 





THE INTEROEOSSING OP EEEATIOS IN GLAOI 



DEPOSITS. 



By JAMES GEIKIE, LL.D., F.R.S., F.G.S., 

 Of H.M. Geological Survey of Scotland. 



{Continued from page 200. ) i£ 





> 



NO one of late years has been more assiduous in the collec- 

 tion of facts relating to the intercrossing of erratics in the 

 drift-deposits of England than Mr D. Mackintosh. He has written 

 many instructive and interesting descriptions of the phenomena 

 in question, which he justly thinks are of prime importance from 

 a theoretical point of view. In a recent paper 1 he presents us 

 with the results of a systematic survey of the direction and 

 limits of dispersion of the erratics of the west of England and 

 east of Wales, which he evidently is of opinion afford strong 

 support to the iceberg theory, while at the same time they are 

 directly opposed to the theory of transport by land-ice. I have 

 attentively considered all the arguments advanced by Mr Mac- 

 kintosh in favour of his views — the one upon which he appar- 

 ently lays most stress being that of the intercrossings of erratics 

 observed by him — and I shall now proceed to point out how the 

 phenomena described by him are most satisfactorily explained 

 by the land-ice theory. They seem to me, indeed, to lend ad- 

 ditional support to that theory, in the same manner as the inter- 

 crossings of boulders observed in Scotland, Northern Germany, 

 &c, and the sub-alpine regions of France. Mr Mackintosh 

 calls attention to the fact that erratics of the well-known Criffel 

 granite are found scattered over a large part of the plain of Cum- 

 berland, from which they extend south along the coast to near the 

 mouth of the estuary of the Duddon. They reappear again on 

 the coast in the neighbourhood of Blackpool and Liverpool, and 

 at intervals on the coasts of North Wales from Flint to Colwyn 

 Bay, and thence to Penmaenmawr and the neighbourhood of 

 Beaumaris. They are dispersed over the peninsula of Wirral 

 1 ' Quart. Journ. Geol. Soc.,'vol. xxxv. p. 425. 

 VOL. VI. Q 



