272 NEOZOIC TIME. [CHAP. XIII. 



belong to the older Glacial series, and when we reach the 

 districts which are occupied by the newer Boulder-clays, 

 river-gravels are not so extensively developed, and appear 

 to be comparable only with the later river-deposits of 

 southern England, for they do not contain Palaeolithic im- 

 plements or the fauna of the older southern gravels. 

 Moreover, Cyrena fluminalis and remains of some of the 

 older mammals have been found in Lincolnshire and York- 

 shire beneath the highest sheet of Boulder-clay a fact 

 which raises the presumption that some of the so-called 

 Post-glacial gravels may have been contemporaneous with 

 the latest Glacial deposits on either side the Pennine 

 Hills. 1 



The same assemblage of animals which occurs in the 

 older river-gravels is also found in the lower layers of the 

 cave-earths throughout the country, and it has been sur- 

 mised that many of these caves date from a period ante- 

 rior to the later Glacial deposits of northern England. In 

 the case of certain caves in the valley of the Clwyd in 

 North Wales, it is asserted that these deposits are banked 

 against the entrance of the cave in which mammalian 

 bones and flint implements have been found ; but the 

 exact relation of the inside and outside deposits is still a. 

 matter of doubt. 



The old river-gravels are found in patches and terraces 

 which are as much as 80 or 100 feet above the level of the 

 nearest stream, and it is difficult to understand how the 

 rivers can have deepened their valleys to such an extent 

 since the formation of the gravels unless the land stood 

 for a long time at a much higher level than it does now. 

 This conclusion is confirmed by the depth of the valley- 

 beds below the sea-level near the coast, in some cases 

 amounting to 70 or 80 feet, for it is obvious that the stream 



1 This was first suggested by Professor J. Geikie, see ' The Great 

 Ice Age," second edition, p. 526. 



