GEOLOGY carried onward by the ice. The clays are in many places used for bricks. The intercalated sands occur in masses sometimes exceeding a hundred feet in thickness, and are generally clean red, yellow, or buff sands, sometimes free of pebbles, but more often containing lenticles of gravel. They have been a favourite source for local water supplies, and the sites of many of the villages such as Betley, Wrinehill and Madeley were no doubt originally selected for this reason. It was originally thought, and the opinion is still sometimes upheld, that the clays and sands maintain a definite relationship. Thus there is considered to be an old stiff clay full of scratched stones (Till or Lower Boulder Clay] on which the sands and gravels (Middle Glacial Sands] rest. The latter have been taken by some glacialists to indicate an amelioration of climate and depression, followed by a re-elevation and second refrigeration represented by an overlying sheet of clay (Upper Boulder Clay). In the Trent basin Mr. Deeley 1 introduces further sub-divisions, each of which he regards as indicative of different stages of glaciation. Though this threefold sub- division can be frequently observed, it is commonly acknowledged that the presence of the three members at any one spot is accidental, while one or even two are as often absent as present. Both sands and clays, but more frequently the coarser bands of sand and lenticles of gravel, contain fragments of recent marine shells of types met with in the Irish Sea and in more northern waters. An entire specimen is the exception, the merest fragments being generally met with. Faint glacial stria? can sometimes be observed on the larger fragments. The commonest shells and fragments are cockle (Cardium edu/e), Mytilus edu/is, Turritella terebra^ Tellina balthica, Cyprina, My a. They are to be found in fair abundance round Wolverhampton, Madeley (Staffs), from Woore to Alsager, and near Biddulph, in pits opened in the clays and sands. North Sea Glacier. While the Irish Sea basin was filling up with ice, the North Sea, fed with glaciers from Scandinavia, was likewise being piled thick with ice which reached the English coast a little north of Flamborough Head. Sweeping inland it crossed the Trent at Gains- borough, and thence pushed its way up the Trent valley to Derby and Burton-on-Trent. Its influence on Staffordshire is scarcely appreciable, though it exercised a strong hold on Leicestershire. Passing as it did over the Jurassic and Cretaceous deposits of the eastern counties, its debris, gathered from these rocks, is at once distinguishable from the fragments of Palasozoic rocks brought into the county by the Irish Sea glacier. Flints, Chalk and fragments of the Lias and Oolites, mingled with an occasional Scandinavian gneiss or igneous rock, at once betray the presence of the North Sea ice. Only its fringe however reached Staffordshire, and scattered its far distant collected rocks around Burton-on-Trent, Abbots Bromley and possibly even as far west as Uttoxeter, though here the flinty gravel may in part be attributed to material washed out of the eastern ice. 1 'The Pleistocene Succession in the Trent Basin,' Quart. Journ. Geol. Soc. xlii. 437 (1886). 29
