1 62 UNIVERSITY OF COLORADO STUDIES 



resemble those of the present day. During the Miocene, the lowlands 

 were occupied largely by a flora which has not been able to survive 

 the later cold, and has either been exterminated or driven into Central 

 America. But in the mountains, the temperate region flora must 

 have maintained itself, restricted in area, but ready in a later day to 

 spread widely over the country. Hence assuming the Florissant beds 

 to be Miocene, their plants might show more similarity in many res- 

 pects to those of today, than to the strictly contemporaneous flora of 

 the lowlands in the same latitude. 



It is true that Scudder refers a number of times to subtropical affini- 

 ties exhibited by the Florissant insects, but on the whole the insect 

 fauna is that of a warm temperate region; and certainly the bees, 

 which I have studied, are by no means of tropical groups. The preva- 

 lence of Aphides indicates a temperate region, while many of the genera 

 in other groups are such as exist in the United States today. The 

 appearance of a small number of species having a really tropical jacies 

 is explained by the ready migration of insects; and, in truth, such 

 forms exist in the Colorado fauna today, some as permanent residents, 

 others as casual visitors. 



It is much to be regretted, that in all the collecting which has been 

 done at Florissant, no record has been kept of the exact horizons from 

 which the specimens came. It may well be that the plants and animals 

 are not the same in all, and that much time elapsed between the for- 

 mation of some of them. This seems the more probable, from the 

 large number of closely-allied species of certain groups of insects and 

 plants; too many, it would seem, to have existed at the same time 

 and in the same immediate locality. If these could be ascertained 

 to come from different horizons, the difficulty would be explained. 

 There is also reason to hope that by carefully noting the horizons we 

 might determine the time of year of the eruptions. Lesquereux has 

 already made some suggestions bearing upon this matter; and it is 

 to be remarked that large numbers of Bibionid flies and winged Ter- 

 mites have been found, indicating by their presence early spring. If 

 we could thus ascertain the time of year of any particular layer, we 

 should know something about the time of flight of the insects entombed 



