HISTORY OF THE LINDEN AND ASH 167 



and the familiarly cultivated mountain ash of America and 

 Europe are related species of the genus Sorbus and belong to the 

 Rose family (Rosaceae), in fact none of these that I have enu- 

 merated belong to the same plant family as the true ash. 



The earliest fossils that have been referred to the ash (Frax- 

 inus) are leaves, whose identity is not conclusive, from what are 

 called the Patoot beds of western Greenland. These deposits 

 are of late Upper Cretaceous age and are underlain in that 

 region b}^ the older Atane beds which also contain an extensive 

 flora with walnuts, figs, magnolias, persimmons, poplars and 

 other species of ancestral trees, but no traces of ashes. The 

 correctness of the identification of these Patoot species of ash is 

 really of but slight importance for these deposits are immediately 

 overlain by a series of lignitic shales and basalts of early Tertiary 

 age and an abundant flora is found associated with the lignite 

 in which the leaves of an ash are found. These leaves are almost 

 certainly those of an ash since they also occur in the Eocene of 

 southeastern North America associated with characteristic ash 

 fruits. The history of Fraxinus thus is known to go back at 

 least as far as the dawn of the Tertiary period, an epoch esti- 

 mated to date from at least three million years ago, to a time 

 which antedates the appearance of the ancestral polydactyl 

 horses, or for that matter any of the lines leading to the higher 

 mammalia. 



About a dozen Eocene species of Fraxinus are known. They 

 are found from Greenland to Louisiana and from Alaska to 

 Oregon, Colorado and Wyoming. Their remains include leaves 

 and characteristic fruits, specimens of both of which of this age 

 are shown on the accompanying plate. All of these Eocene 

 forms that have thus far been discovered are either North 

 American or Arctic American — none having been found in the 

 abundant Eocene floras of Eurasia. It therefore seems probable 

 that the genus originated at some time during the late Cre- 

 taceous on either the North American mainland or in the region 

 immediately to the north of it. Very little is known of the 

 geologic history of plants in the vast region of Asia, but if the 

 ash had originated on the latter continent it should have spread 



