Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/904

 seen on the northern side of Morecambe Bay is no doubt due to the stranding of ice-bergs.

9. That the surface of the Middle Drift in Lancashire appears to have been everywhere eroded into small hollows and undulations, apparently caused by subaerial denudation ; if this be so (and there are many reasons to believe it was), the country must have risen above the Middle-drift sea, become land, have suffered denudation, and again sunk beneath the sea before the deposition of the Upper Boulder- clay. Be that as it may, there can be no doubt that the Upper Till invariably rests on an eroded surface of Middle Drift, the two formations being unconformable.

10. That at the close of the period during which the Middle Drift became eroded, the climate again became cold, and that portion of land which stood above the sea more or less covered with ice ; this tract was probably considerable, as the land during the deepest submergence of the Upper-till period does not appear to have been more than 800 feet lower than at present, the clays in the deeper valleys of the Penine chain, at greater elevations, probably belonging to the high-level Lower Boulder-clay. With the change of climate came an alteration in the character of the deposits ; sands and gravels were no longer thrown down, owing probably to the coasts being again surrounded by an ice-foot ; and the grinding of glaciers over the land caused vast quantities of clay to be carried out to sea, held in suspension by the water, and spread over the country, where stratification is now but faintly visible, probably from the extreme fineness of the grains of matter of which the Upper Till is composed : the included stones in it, though erratic, are always more or less rounded ; and at whatever height, so far as I have seen it, this formation occurs, it invariably contains more or less perfect shells of marine mollusca. None of these are of an extremely arctic character, Turritella communis, Buccinum undatum, Purpura Lapillus, Cardium edule, and Tellina balthica being the commonest. All these occur in the Middle Drift, as well as many others. The first also occurs in the marine Lower Boulder-clay, and also in the Upper Till.

11. That before the surface of the Upper Boulder-clay became land, and probably before any upward movement commenced, the climate appears to have ameliorated, the ice-foot to have disappeared, the formation of shingle to have recommenced, and the glaciers to have sufficiently retreated to no longer send down vast quantities of clay to the sea, the dust, so to speak, of their gigantic sawing of the valleys of the country ; for on the surface of the Upper Till, in the north of Lancashire, often at elevations of 500 or 600 feet, occur mounds of water- worn gravels, similar to those known as Kames in Scotland, and Eskers in Ireland.

12. That the glaciers appear to have lingered especially in the deep valleys of the Cumberland and Westmoreland lake district, where, in many cases (Borrodale, Langdale, Liza valley), they have excavated out the marine drift, and shed their moraines in the space thus left vacant. In the latter valley I found the moraine- mounds to be peculiarly numerous and well preserved.