Pleistocene. But while the fact of the human remains 

 having been discovered above the boulder-clay appears 

 to point to a post-glacial date, still there is con- 

 fronting us the perplexing anomaly of the contemporary 

 existence of extinct mammals belonging to a tropical 

 fauna, which, if we accept this theory, involves the ne- 

 cessity of admitting that a tropical climate followed the 

 last glacial epoch a condition of things that we know 

 never existed at all. The fact is there have been more 

 periods of glaciation than one, each being followed by 

 the deposition of boulder-clays ; and between the periods 

 of intense Arctic cold there were intervals of tropical or 

 sub-tropical heat, when mammals belonging to and 

 requiring a tropical climate ventured as far north as 

 the north of England, to become extinct when the period 

 of glaciation supervened. The last glacial period, we 

 know, extended its area of influence as far as the high 

 peaks of Switzerland and Northern Italy, completely 

 overwhelming the whole of Northern Europe as far south 

 as the latitude of 45, and the whole of North America 

 as far south as the latitude of 40 ; since when there has 

 been a gradual diminution of cold until the present tem- 

 perate climate supervened. Now, if it can be positively 

 ascertained that all the boulder-clays found in England 

 and Northern Europe were deposited during and imme- 

 diately after this last glacial period, the date of man's 

 first appearance in those districts, as far as we have as 

 yet any evidence, must be post-glacial ; but in such a 

 case it would have been impossible that a tropical fauna 

 and flora could have existed in the same localities, 

 whereas their remains have been abundantly found lying 

 side by side with the remains of Palaeolithic man. The 

 conclusion we must draw is that the boulder-clays found 

 below the remains of Palaeolithic man could not have 

 been deposited after the last period of glaciation, but 

 must have followed some prior glacial condition, and 

 that man existed in England and Northern Europe con- 

 temporaneously with extinct mammalia during inter- 

 glacial or pre-glacial times, when the climate of England 

 was tropical or sub-tropical that is to say, in middle 

 Pleistocene or late Pleiocene times. If man really 

 existed in England in Pleiocene times, in favour o 



