196 The Scottish Naturalist. 



Recently Messrs B. N. Peach and }. Home, in a most 

 instructive paper on the " Glaciation of Caithness," 1 have 

 described some remarkable comminglings of material which 

 occur in a region where the glacial striae afford equally striking 

 evidence of conflicting ice-movements. These phenomena are 

 developed here and there along a line which indicates the meet- 

 ing-place of two rival ice-streams, on each side of which the 

 boulder-clay presents different characteristics — the one boulder- 

 clay being the moraine profonde of the ice that flowed E.N.E. 

 and N.N.E. towards the Caithness plain, while the other is an 

 accumulation formed underneath the ice that streamed across 

 that plain from S.E. to N.W. These phenomena are thus, as 

 my colleagues remark, quite analogous to those met with in the 

 middle districts of Scotland, as described by me, and referred 

 to in a preceding paragraph. Now it is obvious, that while 

 these examples of " intercrossings " of erratics and "cross- 

 hatching " of striae all go strongly to support the land-ice theory 

 of the glacial phenomena, they at the same time negative the 

 notion of floating- ice having had anything to do with the pro- 

 duction of the phenomena under review. 



Before considering the evidence adduced by Mr Mackintosh 

 and others as to the intercrossings of erratics in the drift- 

 deposits of England, I shall mention some of the more re- 

 markable examples of the same phenomena which have been 

 noticed by Continental geologists. The first I shall cite are 

 those which have been observed in the glacial accumulations 

 of the Rhone valley in Eastern France. The land-ice origin of 

 these accumulations has never been called in question, and as 

 the intercrossings of erratics in that region are not only more 

 common, but much more striking and apparently inexplicable 

 than any which have been noticed elsewhere, it will be admitted 

 that they of themselves afford a strong presumption that the 

 conflicting courses followed by the erratics in certain regions of 

 our own country are the result rather of oscillations in the flow 



least as Fife — erratics of Fifeshire rocks occurring in the till of the Shet- 

 lands. Many facts connected with the glacial geology of Perthshire and 

 Forfarshire have led me to the same conclusion. I believe, however, that 

 the ice-sheet of an earlier cold epoch of the Glacial Period (represented as I 

 think hy the grey till just referred to) flowed south rather than north in the 

 bed of the North Sea, from some point probably as far north as Aberdeen- 

 shire. Put the facts upon which this belief is grounded are too numerous 

 and detailed to be given here. 



1 Proc. Royal Physical Society, Edinburgh, 1881. 



