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Rh Evidently it lies unconformably on the Purbeck and older strata, and yet curiously enough in some of the lower bands of ferruginous sandstone there have been found remains of freshwater shells, Unio, Cyrena and Paludina, which led Fitton, John Phillips and also Prestwich to regard these beds as of Wealden age. Now elsewhere, where Wealden Beds occur, they are comformable with the Purbeck Beds, and the explanation given by other geologists, that these fossiliferous layers are freshwater beds of Lower Greensand age seems most reason- able.

It may be remarked that John Morris noted the occurrence of freshwater mollusca at Hartwell, and he mentioned the finding of the Wealden plant, Endogenites erosa, near Stone church, probably at the base of the sands. (1867). At Muswell Hill Unio porrectus, a Wealden species, has been found. We have however no grounds for concluding that Wealden species of freshwater mollusca died out at the close of the Wealden period, and the stratigraphical evidence is in favour of group- ing with the Lower Greensand all the strata about to be described which occur between Shotover and Woburn. It may be useful to group, as Mr. A. M. Davies has done, the beds at Muswell Hill, Brill, Long Crendon, Oving and Quainton under the old name of Shotover Beds. These beds attain a thickness of about 50 feet.

Elsewhere near Aylesbury, at Bishopstone, Haddenham and Stone the sands and hard ferruginous layers have yielded impressions of marine Lower Greensand fossils, Exogyra sinuata, Lima and Pecten, and these beds, which may belong to a newer stage than the Shotover Beds, are grouped as Bishopstone Beds by Mr. Davies.

The precise relation of these two divisions to the thick mass of Woburn Sands may well be left an open questionprobably both are represented in that thick series.

Much of the Lower Greensand in the outlying hills consists of coarse and fine sands 20 feet or more thick with hard concretionary masses, the sand being in places clean and white, and adapted as near Stone for glass-making, for which purpose it was formerly sent to Birmingham. At Stone it is cemented in places into hard and irregular siliceous concretions of such grotesque forms that they are known as ' bowel stones.' Elsewhere the sands are of various tints, some red and orange-coloured, the coarser sands containing pebbles of quartz, quartzite and lydian stone. Thin seams of ironstone occur as well as beds of clay, while fuller's earth and ochre were formerly dug at Brill, and whitish pipeclay is met with at Oving.

The soil in general is a reddish brown sandy loam, and the strata are usually water-bearing, having at Stone furnished a good supply. Further on towards Woburn, where there is a greater thickness of the sands, larger permanent supplies of water may be expected, but that