232 TREE ANCESTORS 



species, and include at least two European and two American 

 forms. These all occur either far to the southward of the ice 

 sheets, as for example Fraxinus ornus in Italy, or in Interglacial 

 deposits, as for example Fraxinus excelsior in France and Germany. 

 In this country our white ash, Fraxinus americana, is found in 

 the early Pleistocene of western Kentucky and the late Pleistocene 

 of Maryland; the existing blue ash {Fraxinus quadrangulata) of 

 the Mississippi valley was present and pushed northward as far 

 as the Don Valley in Canada during an Interglacial period when 

 the climate for a time was somewhat warmer than it is at the 

 present time in the same latitude. 



