William Henry Penning

“ In submitting to the consideration of the Society the following observations, I would remark that they are intended to form, not a full description, but a sketch of the physical geology of East Anglia during the glacial period. ”

“ Arctic conditions of climate began to prevail; and here and there patches of clay were dropped by icebergs, heralds of those to follow in such vast numbers during the Upper Glacial epoch. The contorted drift, which occupies a large area in the north-east portion of the district, was deposited during the early part of this submergence of the land; its mode of formation I consider to have been much the same as that of the Upper Boulder-clay presently to be considered. The contortions sometimes exhibited by this deposit are probably due to agencies acting on the clay at a subsequent period. ”

“ To some extent, and in small areas, this may be so; but looking at the Boulder-clay as a whole, there is a striking regularity in its occurrence. When viewed on a true scale, in the exceptional case of the Chalk escarpment it is seen to plunge down about 500 feet; but this being in a distance of not less than 10 miles, represents a fall of 1 in 100 only, or an angle of about half a degree. It touches, as any other formation would be expected to do, the outliers and hills within the larger valley which are sufficiently high to reach its horizon ”

“ In the gravels are intercalated occasional masses of Boulder-clay which were brought down by icebergs, and which, heavily descending from them, have distorted the gravels wherein they now lie without any approach to order or arrangement. Further evidence of icebergs during this period is found in the associated series, or parts of series, of fossil remains taken from the gravels—as, for instance, at Bishop Stortford, where a good number of vertebræ and other bones of Pliosaurus, parts of the same animal, were discovered. ”

“ Throughout are interspersed masses of current-bedded sand and occasional patches of iceborne clay.
The general absence from these beds of fossil remains may be ac- counted for by the conditions of deposit; they were formed in a strong current, which would be (except, perhaps, at the commencement and end of the period) unfavourable to the existence of animal life, while the remains of any plants or animals that may have come within its sweep would speedily be reduced by attrition, except of course those which were previously fossilized, and all of which are much rolled and waterworn. ”

“ North of Cambridge it opens out into a broad expanse of fen-land, overlooked from the east side only by the high chalk range. Rarely do any beds lower than the Neocomian crop out; but by these and the Gault the Fen is skirted all the way to the sea.
The Chalk escarpment receded to its present position or thereabouts in the Pliocene period: during the progress of its submergence for, and reelevation after, the Eocene deposits it had been subjected to some disturbance, many small faults, flexures, and contortions being the result. ”

“ Upper Glacial.—The Great Chalky Boulder-clay in East Anglia extends in mass, or in patches that once formed part of the main mass, over the northern half of the London Basin, the Pliocene area, and the dip slope of the Chalk, rises over the escarpment of the same formation, and plunges down into the Cambridge valley. ”

“ Much has been already written about them; they have now been mapped by the Geological-Survey Officers, and will be fully described by them also in their publications. The same remark applies to the Fen-lands, which are of more recent date than the Drifts proper that form the subject of this communication. ”