654 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 22, 
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 forma- 
tions 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 thon 800 feet lower than at present, the clays in the deeper 
valleys of the Penine chain, at greater elevations, probably belong- 
ing to the high-level Lower Boulder-clay. With the change of cli- 
mate 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 cha- 
racter, Z'urritella communis, Buceinum undatum, Purpura lapillus, 
Cardium edule, and Tellina balthica being the commonest. All these 
occur inthe 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 commeneed, 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 preseryed. 
