Before going further it will be well to explain and limit more definitely the field of our present enquiry. It may be said that there are "submerged forests" of various geological dates, and this is perfectly true. The "dirt-bed" of the Isle of Purbeck, with its upright cycad-stems, was at one time a true submerged forest, for it is overlain by various marine strata, and during the succeeding Cretaceous period it was probably submerged thousands of feet. Every coal seam with its underlying soil or "underclay" penetrated by stigmarian roots was also once a submerged forest. Usage, however, limits the term to the more recent strata of this nature, and to these we will for the present confine our attention. We do not undertake a description of the earlier Cromer Forest-bed, or even of the Pleistocene submerged forests containing bones of elephant and rhinoceros and shells of Corbicula fluminalis. These deposits will, however, be referred to where from their position they are liable to be confounded with others of later date.
CHAPTER II
THE THAMES VALLEY
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.
