THE FOREST PERIOD.
Subsequently to Palæolithic times, the physical conditions over Eurasia changed greatly, and at the commencement of Neolithic times the conditions were favourable for the growth of forests over wide regions of that continent. At the commencement of the Forest period the physical conditions were very much the same as they are at present, though minor changes have of course taken place since then, including probably a submergence of large parts of Britain to a depth of about fifty feet beneath its former level, as indicated by the existence of Neolithic submerged forests round many parts of our coast-lines.
The Forest period may be best subdivided for local purposes by reference to the civilisation of mankind at different times, and in this way we obtain the following divisions:
Historic Iron age.
Prehistoric Iron age.
Bronze age.
Neolithic age.
A classification may also be based upon changes in the flora. In Denmark the peat deposits of this age are divisible into five layers, characterised by different dominant forms of trees. These are as follows in descending order:
| Fifth layer: | Beech | ... | Iron age |
| Fourth layer: | Alder | ||
| Third layer: | Oak | ... | Bronze age |
| Second layer: | Scotch Firs | ... | Neolithic age |
| Lowest layer: | Poplar. | ||
In our own country the forest growth has been much interfered with by man, but the lower fenland peat gives a good example of the material formed by forest growth. It is not necessary to touch on the various accumulations which are now being formed in different parts of our island, except to remark that the deposits of the Forest period give indications of earth-movements on a small scale, which is well seen in the fenland, where the forest peat is covered in places by a "buttery clay" with Scrobicularia piperata indicating submergence, and above this is a marsh peat.