230 TREE ANCESTORS 



The history of the ash is hence known to go back at least as far 

 as the dawn of the Tertiary period, an interval of several milHon 

 years, to a time antedating the five toed ancestral horses, or for 

 that matter any of the lines leading to the higher mammalia. 



About a dozen Eocene species of ash are known. They are 

 found from Greenland to Louisiana, and from Alaska to Oregon, 

 Colorado and Wyoming. Their remains include leaves and char- 

 acteristic fruits or ash-paddles. Eocene species of both of which are 

 much like their modern relatives. All of these Eocene forms 

 that have thus far been discovered are either North American or 

 Arctic American — none having as yet been found in the abundant 

 Eocene floras of Europe, and Asia being practically unknown. 

 Undoubtedly there were Eocene ashes in northeastern Asia for we 

 find there many of the forms found at that time on this side of 

 Behring strait in Alaska. We may tentatively assume that the 

 ash originated at some time during the late Cretaceous on the North 

 American mainland or in the region north of it. Very little is known 

 of the geologic history of plants in the vast region of Asia, as already 

 remarked, but if the ash had originated on the latter continent it 

 should have spread to Europe, where Eocene plant beds are so 

 common, about as quickly as it cHd to North America. This fact 

 and the large number of American Eocene species fortify the 

 conclusion that the early ash was an American product. 



However, the ash was well on its way toward Europe for during 

 the succeeding Oligocene the leaves and fruits are found at a 

 large number of localities on that continent, from the amber 

 beds on the shores of the Baltic to the gypsum beds along the 

 shores of the Gulf of Lyons. Ten dift'erent forms of Oligocene 

 ash are known and these are all European, since Asia remains 

 unknown and in North America the deposits of Oligocene age are 

 largely marine marls or limestones along the continental borders 

 or flood plain and channel deposits in the interior in Vv^hich fossil 

 plants seem to be rarely found. Tv/o fruits of Oligocene ashes 

 from Europe are shown on the accompanying plate. 



Passing to Miocene times, which succeeded those of the Oligo- 

 cene, we find Fraxinus, like most of the other tree genera, to have 



