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Thus, a flood of light was thrown on a subject which had puzzled even the late Professor Edward Forbes, who suggested the "ploughing up action of ice-burgs, and the sweeping action of great waves coming from the north." But the mud of the boulder clays required a still sea for its deposition; and its depth in Lancashire and Cheshire may be judged from the fact that the upper boulder clay of Macclesfield is 700 feet, and of Arnfield, Cheshire, upwards of 600 feet above the sea level; yet the broken and fragmentary shells of the Mollusca occur throughout at all levels, and are all littoral or sub-littoral in their habits—some living on rocks, others on sand, others on sea-weeds, yet found in a common matrix of red clay—none of the bivalves with valves united, and all more or less broken.

The presence of the glaciated erratics and arctic Mollusca tells us the climate was severe enough for the formation of ice in the winters along the then shores, when the north of England was sunk, perhaps, a thousand feet or more beneath the glacial sea; when glaciers ground their way down the valleys of Wales and the Lake district, sending forth their turbid streams of mud into the sea to form the boulder clays. Along these shores lived the Mollusca; from these shores the ice-rafts distributed them over the sea-bed. together with the glaciated stones with which they lie entombed, which bed, since upraised, has become the plains of Lancashire, Cheshire, and, perhaps, the Midland Counties. The granite boulders in the boulder clays of Lancashire and Cheshire have been traced to their sources in Eskdale, Cumberland, and Criffel, Scotland; and their distribution extends far beyond the limits of these counties, in a southerly direction. There is, therefore, a fair field of research open to the Midland Geologist in the boulder clays of those districts. The boulder clays of the north-west of England were once thought to be azoic, yet they have yielded to research a large fauna. In the upper boulder clay of Newton-by-Chester, I have found 148 species of Mollusca, Ostracoda, Foraminifera, &c., where no one thought of looking for a shell before 1873.

A word or two in conclusion may be spared for the middle sands and gravels, which occupy considerable areas in Lancashire and Cheshire. Professor Hull, M.A., F.R.S., was the first to observe that the drift clays and sands and gravels could be separated into three divisions—1st, in descending order—an upper boulder clay; then, 2nd, this way succeeded by (middle) sands and gravels; and, 3rd, a lower boulder clay. The physical features and the fauna of the upper and lower boulder clays are very similar, except that the lower boulder clay bears evidence of more glacial conditions than the upper. All the phenomena I have described are applicable to both clays. The middle sands and gravels differ from the boulder clays—first from the total absence in them (except near the mountains) of glaciated clays. The shells, too, of the Gastropoda are not filled with Microzoa, like those of the clays, it with the course sand or the gravel, in which they are generally found embedded. The rolled character of the broken shells of the Molluscs also points to a different mode of distribution to those of the boulder clays.