In the last chapter an attempt was made to give a general idea of the nature of the deposits; we will now give actual examples of what has been seen. Unfortunately we cannot say “what can be seen,” for the lower submerged forests are only visible in dock excavations. As these works are carried well below the sea-level and have to be kept dry by pumping, it is impossible for them to remain open long, and though new excavations are constantly being made, the old ones are nearly always hidden within a few weeks of their becoming visible. Of course these remarks do not apply to the highest of these submerged land-surfaces, which can be examined again and again between tide-marks, whenever the tide is favourable and the sand of the foreshore has been swept away.
The most convenient way of dealing with the evidence will perhaps be to describe first what has been seen in the estuary of the Thames. Then in later chapters we will take the localities on our east coast and connected with the North Sea basin. Next we will speak of those on the Irish Sea and English Channel. Lastly, the numerous exposures on the west or Atlantic coast will require notice, and with them may be taken the corresponding deposits on the French coast. Each of these groups will require a separate chapter.
The Thames near London forms a convenient starting point, for the numerous dock-excavations, tunnels, deep drains and dredgings have laid open the structure of this valley and its deposits in an exceptionally complete way. The published accounts of the excavations in the Thames Valley are so voluminous that it is impossible here to deal with them in any detail; we must therefore confine ourselves to those which best illustrate the points we have in view, choosing modern excavations which have been carefully watched, noted, and collected from rather than ancient ones.
We cannot do better than take as an illustration of the mode of occurrence and levels of the submerged land-surfaces the section seen in the excavation of Tilbury Docks, for this was most carefully noted by the engineers, and was visited by two competent observers, Messrs. W. Whitaker and F. C. J. Spurrell. This excavation is of great scientific importance, for it led to the discovery of a human skeleton beneath three distinct layers of submerged peat, and these remains have been most carefully studied by Owen and Huxley, and more recently by Professor Keith.
The section communicated to Sir Richard Owen by Mr Donald Baynes, the engineer superintending the excavation at the time of the discovery, is shown in the diagram on p. 14. As Mr Baynes himself saw part of the skeleton in the deposit, his measured section is most important as showing its exact relation to the submerged forests. It is also well supplemented by the careful study of the different layers made by Mr Spurrell, for though his specimens did not come from exactly this part of the docks, the various beds are traceable over so large an area that there is no doubt as to their continuity.
| Trinity High Water Level | |||
| Water 6’·77 | |||
| Marsh Level | |||
| 1 | Clay 6’·04 | ||
| 2 | Mud 10’·76 | ||
| 3 | Mud and Peat 1’·70 | ||
| 4 | Peat 1’·08 | ||
| 5 | Mud 3’·88 | 34’·54 | |
| 6 | Peat 3’·58 | ||
| 7 | Mud 1’·76 | ||
| 8 | Mud and Peat 3’·24 | ||
| 9 | Sand & Decomposed Wood ·62 | ||
| Level at which human remains were found | |||
| 9* | Sand 12’·47 | ||
| 10 | Ballast Gravel |
Fig. 2. Section at Tilbury Docks.
Owen thought that this skeleton belonged to a man of the Palaeolithic period, considering it contemporaneous with the mammoth and rhinoceros found elsewhere in the neighbourhood. Other geological writers showed however that these deposits were much more modern, and some of them spoke somewhat contemptuously of their extremely recent date. But Huxley saw the importance of this “river-drift man” as an ancient and peculiar race, and Professor Keith has more recently drawn especial attention to the well-marked characteristics of the type. The skeleton is not of Palaeolithic date, but neither is it truly modern; other examples have turned up in similar deposits elsewhere.
We will now describe more fully the successive layers met with in Tilbury Docks, condensing the account from that given by Messrs. Spurrell and Whitaker, and using where possible the numbers attached by the engineer to the successive beds.