The fossils of the times between the Glacial period and the Neolithic period indicate variations of climatic conditions. Upon this point I cannot do better than quote the words of Sir John Evans in his Presidential Address to the British Association at Toronto[117]. "At Hoxne the interval between the deposit of the Boulder clay and of the implement-bearing beds is distinctly proved to have witnessed at least two noteworthy changes in climate. The beds immediately reposing on the clay are characterised by the presence of alder in abundance, of hazel, and yew, as well as by that of numerous flowering plants indicative of a temperate climate very different from that under which the Boulder clay itself was formed. Above these beds characterised by temperate plants, comes a thick and more recent series of strata, in which leaves of the dwarf Arctic willow and birch abound, and which were in all probability deposited under conditions like those of the cold regions of Siberia and North America. "At a higher level, and of more recent date than these--from which they are entirely distinct--are the beds containing the Palæolithic implements, formed in all probability under conditions not essentially different from those of the present day." [Footnote 117: _Report Brit. Assoc._ for 1897, p. 13.] CHAPTER XXIX. 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.