The Lancashire and Cheshire coasts, with their numerous deep estuaries and extensive flats, are noted, however, for their submerged forests, sometimes seen on the foreshore between tide-marks, sometimes laid open in the extensive dock or harbour works. The Heysham Harbour excavations, for instance, were carried far below sea-level and a thin peat-bed was met with in a boring at 52 feet below Ordnance datum. Mellard Reade considered this peat once to have been continuous with an ancient land-surface seen between tide-marks. A boring is not altogether satisfactory evidence for the occurrence of a land-surface at such a depth; but if it is trustworthy it points to a subsidence of about 60 feet, an amount identical with that observed in the Thames Valley.
The estuaries of the Ribble, Mersey, and Dee tell a similar story, for on their shores and under their marshes are found some of the most extensive submerged land-surfaces now traceable in Britain. Many accounts of these have been published; but the alternations of marine with freshwater strata and with land-surfaces are so like those already described that a short account will suffice.
Carefully plotted engineer’s sections will be found in Mellard Reade’s papers, and his account of the succession is so interesting that it is worth quoting. He postulates two periods of elevation, alternating with three periods of depression; but in this area, as in the Thames Valley, it appears as though all the phenomena can be accounted for by one long period of intermittent depression. His generalised section of the deposits in these estuaries is as follows:—
| 3rd period of depression | { | Blown sand |
| Recent silts with beds of peat; Scrobicularia, occasional freshwater shells, red-deer, horse, Bos primigenius, Bos longifrons, and human skull | ||
| 2nd period of elevation | } | Superior peat- and forest-bed |
| 2nd period of depression | { | Formby and Leasowe marine beds; human skeleton, bones of horse and red-deer, Scrobicularia, Tellina baltica, Turritella communis, etc. |
| 1st period of elevation | } | Inferior peat- and forest-bed |
| 1st period of depression | { | Washed drift-sand (apparently no contemporaneous fossils) |
| Boulder clay |
It may be an accidental coincidence; but it is noteworthy that both the Mersey and Thames show two main peat-beds separated by marine strata.
The forest exposed on the foreshore at Leasowe (frontispiece) is a particularly good example of these old land-surfaces, and it is often visible. It evidently once formed a wet, peaty flat on which grew swamp plants, brushwood, and some large trees. Parts of it show a perfect network of the rhizomes of Osmunda. This “superior peat- and forest-bed” was forming when the sea was only a few feet below its present level. The “inferior peat- and forest-bed” probably indicates a drier soil; but it is difficult to get at and requires fuller investigation.
The excavation for an extension of the Barry Docks, in Glamorganshire, exposed in 1895 an interesting succession of deposits, and fortunately a particularly competent observer, Dr Strahan, was on the spot to note them and their exact levels. He also obtained masses of material from each of the beds, and from an examination of the contents of these I was able to gather a clear idea of the changes of sea-level which had affected this part of South Wales. The following sequence was met with:—
| 1. Blown sand. | } | Recent subaerial and tidal deposits. |
| 2. Scrobicularia-clay. | ||
| 3. Sand and gravel with rolled shells (Scrobicularia, Tellina, Cardium, Patella, Littorina). |
Strong line of erosion.
4. Blue silt with many sedges, and at the bottom a few foraminifera.