QUATERNARY DEPOSITS OF BRITISH ISLES BROOKS. 321 



rests either directly on the bowlder clay or on silts and clays with 

 arctic plants. 



The forest bed in this succession evidently corresponds to the 

 superior forest bed of the plains, and to similar beds in Scotland 

 and Ireland ; it points to a period when the climate was much more 

 favorable for tree growth. As it falls in a period of elevation, it was 

 probably a period of continental climate. 



The horizon of the arctic bed is more doubtful. In this district it 

 has not yet been found to be separated from the bowlder clay by any 

 temperate deposits, but, as well-marked arctic beds occur over tem- 

 perate peat in the southern uplands of Scotland and in Holderness, 

 it is probably on the same horizon as the latter, and indicates a return 

 of cold conditions. 



At this point it will be well to review the general evidence in Eng- 

 land for a long interglacial between the formation of the chalky 

 bowlder clay and that of the Hessle clay and other beds of Hessle 

 clay age. Firstly, the surface of the Hessle clay is much more rugged 

 than that of the chalky bowlder clay. The latter forms a level or 

 slightly undulating plateau surface, deeply dissected by the rivers, 

 while the Hessle clay forms a more rugged country with an uneven 

 surface, in the basins of which " meres " are found. The change is 

 very marked in passing from West Norfolk to Holderness. 



Secondly, there is the evidence of weathering. The chalky bowlder 

 clay is so calcareous that it always preserves a grayish tint, but at 

 Finchley the soft chalk which it must once have contained has com- 

 pletely disappeared, and only the hard Lincolnshire chalk remains ; 

 erratics of this are always rounded, and rarely retain even faint 

 striations, though striations often remain on the hard carboniferous 

 limestone. 



Thirdly, there is the evidence of the distribution of the fossil re- 

 mains of the Quaternary mammals. The distribution of the species 

 of Elephas was described, with maps, by Leith Adams (95). Ele- 

 phas antiquus and E. meridionalis occur in association only in the 

 Cromer forest bed. Elephas antiquus and E. primigenius occur asso- 

 ciated at a number of points, all outside the limits of the bowlder 

 clay classed as newer, except the cave earths of Cefn and Gower in 

 Wales. Elephas antiquus never occurs on the surface of the newer 

 glacial deposits. Elephas primigenius, on the other hand, occurs 

 alone over most of England and Wales and the south of Scotland, 

 and is younger than the newer glaciation. 



The association of Elephas antiquus with abundant E. primigenius 

 is characteristic of the " Chelles " fauna, including Rhinoceros me- 

 garhinus, R. leptorhinus, Hippopotamus amphibius, and other spe- 

 cies. The southern limit of the newer bowlder clays also forms the 



