1917] Fossil Insects 9 



in Colorado the end of the Cretaceous marks the emergence of 

 the country east of the mountains from the sea, and the transi- 

 tional marsh conditions, with an abundance of luxuriant 

 vegetation, produced the deposits now yielding the Laramie 

 coal. About this time the great dinosaurs died out, and the 

 higher mammals began to show what they could do. The story 

 of Tertiary mammalian life is a wonderful one, and our knowl- 

 edge of the details is now very considerable. Reasoning from 

 analogy, we might expect that the Tertiary would show a 

 progressive movement in insect evolution comparable with 

 that marking the end of the Palseozoic and beginning of the 

 Mesozoic. It is a fact that on comparing the Tertiary insects 

 with the Mesozoic, there are differences in part resembling 

 those observed among the mammals. The Tertiary insect 

 fauna is essentially modern, indeed it may be said that we have 

 it still with us. It is far richer and more varied than that of 

 the Mesozoic, especially in such groups as Lepidoptera and 

 Hymenoptera. In the flora, we have a remarkable expansion 

 and development of the herbaceous type, but no radical mod- 

 ification comparable with the origin of the higher flowering 

 plants. So also among the insects, we have a great increase in 

 variety, an immense series of adaptive modifications, but 

 nothing to be compared with the origin of the Coleoptera, 

 Diptera, Lepidoptera and Hymenoptera. Has nature partly 

 exhausted her possibilities, new adaptations being limited 

 owing to the very success of the older ones? 



As students of particular groups of insects, we are keenly 

 interested in the evolution of the modern families and genera. 

 As we look at the known Tertiary forms, we are impressed by 

 the number of genera identical with or closely related to those 

 now living, and the extreme scarcity of extinct families, or even 

 subfamilies. There is this to be said, however, that the oldest 

 extensive fauna in Europe is that of the Baltic Amber, in the 

 Lower Oligocene. Back of that, during the vast period repre- 

 sented by the Eocene and Paleocene, there are only a few scat- 

 tered remains, the most instructive being a beautiful dragon fly 

 (TricBschna gossi Campion) from the Upper Eocene (Bagshot 

 Beds) of Bournemouth. In this country we are more fortunate, 

 since the extensive deposits of Green River in Wyoming and 

 White River in western Colorado and eastern Utah are certainly 

 Eocene, not Oligocene as has been sometimes supposed. There 



