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III] more compact, and its surface rise, till it was dry enough for pines. Another subsidence would cause spongy peat again to spread and kill the pine, and so on. Intermittent subsidence seems sufficient to account for all the changes of vegetation we have yet noticed in connexion with these submerged land-surfaces.

Of the fauna of the fen-silts and peats it is very difficult to give any satisfactory account. If we put aside the March and Chatteris marine gravels with Corbicula fluminalis, and the Nar Valley Clay with its northern marine mollusca as being of older date; and if we also reject the marginal gravels with hippopotamus and mammoth as being more ancient, there only remain a few mammals such as the beaver, wolf, wild boar, and certain cetacea, which we can be sure came out of the true fen-deposits. Implements made by man have only been found in the higher layers, and there seems to be no record in this area of a stone implement found below a submerged forest

Submerged forests of the ordinary type are often to be seen between tide-marks on the flat shores of Lincolnshire; but as they still await proper study they need not here detain us, and we will pass on to the next large indentation of the coast-line, the estuary of the Humber.

Here, owing to the excavation of extensive docks,