GEOLOGIC HISTORY OF THE LOCUST 297 



during these ages that succeeded the OUgocene. Ahhough Asia 

 remains an unknown area we have a ghnipse of a small species 

 preserved in the volcanic ash beds of the Florissant lake basin 

 in the heart of the Colorado Rockies, and a second species in 

 Nevada. No less than five species are already known from 

 Miocene Europe, where they are represented as fossils by both 

 leaves and pods. It is especially interesting to note that one 

 of these from the late Miocene of Italy and another closely 

 related fonn of the same age in France are directly ancestral to 

 the existing European Judas-tree, while a second French species 

 (Cercis ameliae Saporta) from the older Miocene of France 

 seems to have been the ancestor of the -existing Cercis japonica 

 Siebold of eastern Asia. There is little direct evidence of the 

 Judas-tree during the succeeding Pliocene times. Since it occurs 

 both before and after the Pliocene in North America it must 

 have been present at that time. In Europe a single Pliocene 

 species is known from France. 



As practically everyone knows, the Pleistocene, which suc- 

 ceeded the Pliocene, was a time of continental ice sheets or 

 glaciers, which played havoc with the floras and faunas, particu- 

 larly in Europe because of the combination of high mountains 

 and seas along its southern border which effectually barred the 

 ebb and flow of life that took place in Asia and North America 

 with the advance and retreat of the successive ice sheets. 

 During the maxmium extent of the ice only a fraction of the 

 Northern Hemisphere was covered and Asia was largely ice-free. 

 The southern limit of the ice in Europe, where the center of 

 accumulation and dispersal was the Scandinavian region, was 

 the Gennan plain. Here in North America the easternmost or 

 Labradoran center of accumulation and dispersal extended its ice 

 fields only as far south as Staten Island on the Atlantic coast, 

 so that there was plenty of room south of the ice for a vast forest 

 and game preserve fo*r the subsequent repopulation of the more 

 northern region. 



There were at least three periods of glaciation which were 

 separated by long intervals during which the ice disappeared 

 except in the far north, and it is in the deposits fonned during 



