240 GEOLOGY. 



The non-placentals. — If the non-placentals of the northern conti- 

 nents had any kinship to the foregoing placental*, they failed to show 

 it by any special awakening in this time of marvelous placental evolu- 

 tion. In the basal Eocene beds there were somewhat more and larger 

 forms than in previous periods, and during the Eocene, early forms of 

 the opossum (Didelphys) appeared in both the Old and New World. 

 The opossum retained this wide distribution until the Miocene, when it 

 disappeared in Europe, but has remained in North and South America 

 to the present time. 



The birds. — If compared with the singular record of the Cretaceous, 

 the deployment of the birds was very marked. So diverse forms as 

 ancestral gulls, herons, flamingoes, albatrosses, buzzards, falcons, eagles, 

 owls, woodcock, quails, plovers, and ostrich-like, flightless birds of great 

 size, with not a few forms of doubtful interpretation, had appeared. 



The reptiles and amphibians. — One of the greatest contrasts in geo- 

 logical history is found in comparing the size, power, and multitude of 

 the Cretaceous land reptiles with those of the following Eocene. Of 

 the great saurian herd of the Mesozoic only a few forms lived over into 

 the very earliest Eocene epoch (Puerco), and these shortly became ex- 

 tinct, and with their extinction the saurians disappeared. True land 

 reptiles seem to have become rare. There were turtles on both land 

 and sea, and some of them attained a large size. There were crocodiles 

 which belonged about equally to land and water; also snakes, some of 

 which were python-like in form and attained large dimensions. The 

 amphibians were present beyond doubt, but, judging from the fossil 

 remains, they formed a very insignificant factor in the fauna. 



The insect life. — When so much must be omitted, it is unwise to 

 dwell on changes that do not have significant bearings on historical 

 progress, and it may now be summarily remarked, on the authority of 

 Scudder, 1 that there has been but little important change in the insect 

 world since the beginning of the Cenozoic era, almost no new orders 

 or even families having appeared, though the genera and species have 

 changed. 



No very significant change is known in the molluscan or other forms 

 of terrestrial life not already noticed, nor in the fresh-water life. 



1 Mon. XXI, U. S. Geol. Surv., 1893; p. 1. 



