Page:Quarterly Journal of the Geological Society of London, vol. 32.djvu/256

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many years past the attention of geologists has been more or less directed to the fact that a marked difference exists in the distribution 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, approaching 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, Tiddeman, 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 phenomena, 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 phenomena 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 communication between the eastern and western sides of the chain, and that the only agency fully meeting the requirements of this supposition 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