Page:Popular Science Monthly Volume 12.djvu/78

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THE POPULAR SCIENCE MONTHLY.

section exposed, and in it the upper bowlder-clay, similar to that shown in Fig. 2, at one end of the pit, gradually changes into a sandy loam with stones and angular patches of sand, not to be distinguished from the deposit named "trail" in Fig. 1.

At Hoxne itself, on the east side of Gold Brook, there is a gravel-pit showing seams of gravel and sand exactly similar to that at Syleham, but surmounted by sandy "trail" instead of by bowlder-clay. The gravel is not to be distinguished from the other, being composed like it of subangular flint-pebbles with rounded ones of quartz and quartzite, and with many small pebbles of chalk in the lowest seams. Notwithstanding this great similarity, Mr. Prestwich considers the beds at Hoxne to have been formed by river-action in post-glacial times; while those at Syleham, being capped by bowlder-clay, he of necessity classifies as middle glacial. Yet I could find no difference whatever in their appearance or composition. In both the pebbles are mostly small and subangular, with some rounded ones of quartz and quartzite. Both contain many small pebbles of chalk in their lowest seams, and both are false-bedded. That one is covered with bowlder-clay and the other by sandy "trail" does not suffice to prove them of different age, for at the Oakley gravel-pit we can trace the same gravels from one end, where the bowlder-clay overlies them, to the other, where the "trail" does so. The middle sands and gravels are generally supposed by geologists to be marine, and it is incredible that deposits due to such different agencies as that of the waves of the ocean beating on a beach and that of a flooded river should be absolutely identical in appearance and composition. But nowhere is either the ocean or any river known to be forming deposits of subangular pebbles, excepting where they are cutting into preexisting beds of the middle glacial series. Both in sea and in river beaches the pebbles are smoothly rounded, and not, as in the gravels under consideration, broken and subangular. Even when we find in the latter rounded pebbles of tertiary age there is often a piece chipped out of them as if they had been dashed violently together. I have had a large number of the pebbles from the gravel at Ealing counted, and find that over eighty per cent, are broken or subangular. I ask where, in the whole world, is such a deposit being formed by existing agencies? Surely, if ordinary floods would produce them, they have had plenty of opportunities of doing so during the past pluvial year; yet where, on the banks of any of our rivers, have the great floods left deposits even approaching in character to those that geologists confidently ascribe to river-action? That they were caused by a great flood I fully believe, though not by that of any river, but by one that swept over the whole country, driving a huge mass of gravel and sand, and leaving them mantling both hills and valleys, holding or covering up the remains of pal├Žolithic man and the great mammals that had lived before the waters were pent up by the Atlantic glacier.