GEOLOGY, 



THE INTERCROSSING OF ERRATICS IN GLAGTAL 



DEPOSITS. 



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



Of H.M. Geological Survey of Scotland. 



AMONG the many phenomena connected with the glacial 

 deposits of this country which have puzzled geologists 

 to account for, there is none more remarkable than the "inter- 

 crossing of erratics." The fact that such wandered blocks have 

 apparently crossed each other's tracks in their journeys, appears 

 at first sight inexplicable on the assumption that their transport 

 has been effected by land -ice. The phenomena in question, 

 therefore, have always been appealed to by those who uphold 

 the iceberg origin of our boulder-clays, &c, as evidence decis- 

 ively in favour of their views. No one can deny that any 

 degree and amount of intercrossing might take place in the 

 case of icebergs. We can readily conceive how floating. ice, 

 detached from a long line of coast, might be compelled by 

 shifting winds and changing -currents to tack about again and 

 again, so as to pursue the most devious course, and scatter their 

 stony burdens in the most erratic manner over the sea-bottom. 

 While, on the other hand, it is quite impossible to understand 

 how a similar irregular distribution of erratics could take place 

 under one and the same glacier, flowing in a determinate direc- 

 tion. It is little wonder, then, that the curious phenomena of 

 the " intercrossing of erratics" should have had much import- 

 ance attached to it by the upholders of the iceberg theory, see- 

 ing that all the other proofs which have been adduced in favour 

 of this theory have only served to demonstrate its insufficiency. 

 Upon the facts connected with the " intercrossing of erratics," 

 the supporters of this time-honoured theory are now making 

 what I must believe is their last stand. I purpose therefore, in 

 this paper, to give a short outline of those facts, with the view 

 of showing that so far from being antagonistic to the land -ice 

 theory, they are in complete harmony with it ; and indeed 



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