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698, especially at high levels, has been regarded by Sir Joseph Prestwich as possibly resulting from the lateral pressure produced by packing and jamming together of blocks of ice, such as may now be witnessed in rivers like the Danube and the Rhine. The "trail and warp" of Mr. Trimmer, those superficial deposits so common over a large portion of this country, which, indeed, constitute so large a portion of the arable soil, seem also, as the Rev. Osmond Fisher has pointed out, to be significant of a severer climate than at present prevails. The "Palæolithic floors," both near London and at Caddington, are buried under a considerable thickness of this "trail." There is moreover a high probability that, at the time of the deposit of the gravels, Britain was still united to the continent; so that, apart from other causes, there was a tendency for the climate to partake more of a continental character than at present, and to induce greater cold in winter and greater heat in summer.

That the existence of enormous glaciers is as indicative of the action of heat, in order to convert the water of the ocean into vapour, as of cold to condense it, has been insisted on by Professor Tyndall, and even more strongly by Professor Frankland. If at the time of the rivers flowing at the high level, Britain was still connected with the continent, it is by no means impossible that the temperature of the seas on either side of the connecting isthmus may have been different. That connected more immediately with the Southern Ocean would have been the warmer of the two, from which a copious supply of vapour would be carried by the southerly winds, and be condensed as rain in its passage northward.

Mr. Alfred Tylor, F.G,S., in his profusely illustrated papers on the Amiens gravel, and on Quaternary gravels, contends for the existence of a "Pluvial period" subsequent to the Glacial, in which the rainfall was far greater than at present, and such a view has much to commend it for acceptance. But when he proceeds to assert that the surface of the Chalk in the valley of the Somme, and in all other valleys of the same character, had assumed its present form prior to the deposition of any of the gravel or loess now to be seen there, and to argue that the whole of the gravels at all levels on the slopes are of one age, and due