184 J. AITKEN ON THE DISTRIBUTION OF DRIFT 



21. Observations on the Unequal Distribution of Drift on op- 

 posite sides of the Pennine Chain, in the country about the source 

 of the river Calder, with Suggestions as to the causes which led 

 to that result, together with some Notices on the High-level 

 Drift in the upper part of the Valley of the river Irwell. 

 By John Aitken, Esq., P.G.S. (Head June 23, 1875.) 



[Abridged.] 



For many years past the attention of geologists has been more or 

 less directed to the fact that a marked difference exists in the distri- 

 bution of drift on opposite sides of the Pennine chain, a difference 

 amounting in some instances to an entire absence of that material on 

 the easterly slopes for many miles from the watershed of the country, 

 and over a considerable portion of its length, notwithstanding that 

 these deposits overspread the great plains of Lancashire and Cheshire 

 in great force, and are found mounting up upon the flanks of those 

 hills on their western sides to very considerable elevations, ap- 

 proaching closely in some cases to the culminating ridge, and in 

 others, where the chain is crossed by intersecting valleys, to some 

 hundreds of feet in excess of the summit-level of these gorges. It 

 would further appear from facts hereafter to be adduced, that 

 although some of these cross valleys attain to only very moderate 

 altitudes, no communication existed during the glacial period of 

 such a character as to permit of the passage of a body of land ice 

 from one side of the chain to the other. Whilst, however, these 

 phenomena have not wholly escaped the notice of those observers 

 who have, more particularly of late years, directed their attention to 

 the surface accumulations of the northern counties of England, 

 allusion having been made to the subject by Messrs. Binney, Tidde- 

 man, Green, Foster, Dakyns, Goodchild, and others, yet no serious 

 attempt has, I believe, so far been made to grapple fully with the 

 subject by any of those who have hitherto given attention to it. 



The subject has long perplexed me, amongst other observers ; and 

 it is only after a lengthened consideration that I have ventured to 

 suggest a theory which, whilst offering an explanation of the pheno- 

 mena, does no violence to any of the well-established principles of 

 physical or geological science. My object, then, in presenting the 

 present communication is to show that the whole of these pheno- 

 mena are explicable on the supposition that, during the flow of the 

 great ice-sheet over this region, these intersecting channels were 

 sealed and blocked up so effectually as to completely cut off all com- 

 munication between the eastern and western sides of the chain, and 

 that the only agency fully meeting the requirements of this supposi- 

 tion is that of ice or snow so consolidated and fixed in the sinuous 

 channels as to remain stationary and inert while the great mass 

 of glacial ice, in two sheets separated by the more elevated portions 



