284 THE AGE OF MAMMALS 



probably Upper rathor than Lower Miocene. Both the plants and insects 

 show a very close general correspondence with those of ffiningen as de- 

 scribed by Hear/ and CEningen is now considered (p. 263) Middle Miocene. 

 The plants of Florissant are in general similar to those of the Colorado 

 uplands and of our southern states; they are in no sense tropical, and 

 there are no palms whatever. Of the more than hundred genera described, 

 many still exist in Colorado, such as pines (Pinus), 'cedars' {Sabina), 

 alders (Almis), oaks (Quercus), rose {Rosa), ash {Fraxinus), grape {Vitis), 

 maple {Acer), sumac {Rhus), thorn {Cratcegus), thistle {Carduus), aster 

 {Aster), Virginia creeper {Parthenocissus). It would be easy by selection 

 of a large series of such plants and also insects, so similar to those of modern 

 Colorado, to conclude that since the Miocene there had been no climatic 

 changes of any moment. Thus the narrow-leafed cottonwood {Populus) 

 is almost exactly like the common tree of the Colorado foothills; and 

 many other examples might be cited. 



On the other hand, mixed with this familiar flora is a very different 

 one, indicative of a warmer, moister climate. The most prominent element 

 of this other flora is the southern one, such as is found in the eastern United 

 States to-day, including several species of the soapberry {Sapindus), sweet 

 fern {Comptonia), sweet gum {Liquid ambar) , two kinds of chestnut {Cas- 

 tania), bass wood {Tilia), several species of holly {Ilex), smoke tree {Cotinus), 

 persimmon {Diospyros), and even one or two of the figs {Ficus).- This 

 flora, however, is not one of the extreme south. 



Other elements in the flora are of minor importance, but include the 

 giant redwood {Sequoia) now of California. With it grew an incense cedar 

 {Heyderia), now found in America only on the Pacific coast; it also sur- 

 vives (a single species) in Asia. The sequoia and incense cedar are both 

 very closely related to their living Californian allies. Several species of 

 Weinmannia represent a shrub still extant in the mountains of the West 

 Indies. The Old World genera of Florissant, not found in America at all 

 to-day, are few and mostly of doubtful identification; perhaps the best 

 case is that of Porana of the order Convolvulacese, now living in the East 

 Indies and fossil also in the European Miocene. "So far as I am able to 

 judge," continues Dr. Cockerell,^ ''the insects tell the same tale as the 

 plants, except that the Old World element is much more definite and in- 

 disputable, though small." The most striking members of this Old World 

 group are two species of the tse-tse fly {Glossina), to-day exclusively African; 

 this is of especial interest in connection with the introduction of African 

 mammals {Mastodon) into the Miocene of North America. One of the 

 orthopterous insects, a sort of large grasshopper, shows resemblances to a 

 living African genus. Certain neuropterous insects, resembling the 'ant- 



1 Heer, O., Flora tertiaria HelvetiiB, Winterthur, 1853-1859; also, Die Urwelt der Schweiz, 

 2d. ed., Zurich, 1873. 



- Letter to the author, March, 1908. 



