PRELIMINARY CONSIDERATIONS. 75 



sub-tropical state of things. Many attempts have 

 been made to reconcile these apparently contra- 

 dictory circumstances ; one of the older views being 

 that while the tropical types of animals lived during 

 a warm interlude, they migrated southwards with 

 the incoming of colder conditions to the arctic type 

 of fauna. Since, however, it has now been ascertained 

 that the remains of both tropical and arctic forms 

 have been found lying side by side in the same bed, 

 it is perfectly certain that such an explanation will 

 not meet the exigencies of the case " (p. 300). 



In Germany the remains of the Siberian mammals 

 occur to a large extent in a pleistocene deposit known 

 as " loess," and the theory has of late years gained 

 ground that the latter is the fine dust-like sand 

 accumulated during an intensely arctic dry climate. 

 That many of the mammals discovered in the " loess" 

 now inhabit the dry steppes of Eastern Europe and 

 North-Western Asia seems to lend support to this 

 supposition; but besides the mammals there are also 

 land and freshwater shells in this deposit. The mol- 

 luscan fauna certainly indicates no steppe-character, 

 according to Dr. Kobelt (b, i. p. 166). 



The attempt to utilise the Siberian migrants to 

 Europe as indicators of a severe climate there, cer- 

 tainly fails to establish conviction. But it may be 

 asked, surely the remains of the Alpine and Arctic 

 plants which have been found in pleistocene deposits 

 must decide this question in favour of one or the 

 other hypothesis? Let us test it. 



