576 ERA OF MIND. 



tion of the numbers of the former was consequently but providing 

 for the appearance of the latter. 



Invertebrates. — As to the time of the first appearance of existing 

 Mollusks, it is known only that 15 to 25 per cent, of Miocene species 

 of marine shells are identical with species now living ; 40 to 90 per 

 cent, of Pliocene ; and all of the Post-tertiary species. This does 

 not necessarily imply that all the species of Mollusks alive now 

 were alive throughout the Post-tertiary ; for out of the 16,000 

 living species only a few hundreds have yet been found in the beds 

 of that period. Future discovery will undoubtedly add much to 

 the number. 



Among Articulates, less than 100 living species from Post-tertiary 

 deposits are known out of the 300,000 now in existence. The two 

 tribes latest in appearance among fossil Insects, and rarest even to 

 the last, are that of the Lepidopters, the tribe of beauty, and that 

 of the Hymenopters, the tribe of utility, highest instincts, and 

 superior rank. The species of these tribes are less likely to become 

 fossilized than those that frequent wet places, where depositions of 

 silt might be in progress. 



Vertebrates. — Very few Fishes, Eeptiles, or Birds of the present 

 era are yet known, from any discovery of fossils, to have existed in 

 the Post-tertiary. The species have thus far been but little searched 

 for. 



Among Mammals, remains of nearly all the species of modern 

 Europe have been found in beds containing some of the extinct 

 Post-tertiary. The number includes the Hare, Eabbit, Beaver, 

 common Rat and Mouse, the Marten, Wild- Cat, Dog, Fox, Stag, 

 Eoebuck, Reindeer, Aurochs, Hog, Horse, and the Glutton and 

 Polar Bear of northern latitudes, besides many others ; and pro- 

 bably all existing species were then distributed much as they are 

 now over Europe. Moreover, in Sicily and Malta remains of some 

 African Mammals have been found. 



Some of the species may date from the early Post-tertiary ; but 

 the majority apparently from the Terrace or transition epoch. 

 Their remains are found in caverns and alluvial beds, associated 

 with bones of the Elephant [E. primigenius), Rhinoceros [R. ticho- 

 rinus), and Irish Elk {Megaceros Hibernicus), and occasionally with 

 those of the Hyena and Cave Bear. In some cases they have pro- 

 bably been mixed by more modern alluvial action ; but in others 

 they lie as they were originally buried. The alluvial beds in Eng- 

 land, France, and Switzerland are more recent than the old Glacial 

 drift, the latter being observed in several places as an inferior de- 

 posit. 



