160 DISTRIBUTION OF EXTINCT ANIMALS. [part ii. 



groups as Carnivora, Perrissodactyle and Artiodactyle Ungulates, 

 Primates, Chiroptera, Rodents, and Marsupials already well 

 marked, but in many of these there is a differentiation into 

 numerous families and genera of diverse character. It is impossi- 

 ble therefore to doubt, that many peculiar forms of mammalia 

 must have lived long anterior to the Eocene period ; but there 

 is unfortunately a great gap in the record between the Eocene 

 and Cretaceous beds, and these latter being for the most part 

 marine continue the gap as regards mammals over an enormous 

 lapse of time. Yet far beyond both these chasms in the Upper 

 Oolitic strata, remains of small mammalia have been found ; 

 again, in the Stonesfield slate, a member of the Lower Oolite, 

 other forms appear. Then comes the marine Lias formation 

 with another huge gap ; but beyond this again in the Upper 

 Trias, the oldest of the secondary formations, mammalian teeth 

 have been discovered in both England and Germany, and these 

 are, as nearly as can be ascertained, of the same age as the 

 Dromatlurium already noticed, from North America. They 

 have bee:i named Microlestes, and show some resemblance to 

 those of the West Australian Myrmecobius. In the Oolitic 

 strata numerous small jawbones have been found, which have 

 served to characterise eight genera, all of which are believed to 

 have been Marsupials, and in some of them a resemblance can be 

 traced to some of the smaller living Australian species. These, 

 however, are mere indications of the number of mammalia that 

 must have lived in the secondary period, so long thought to be 

 exclusively " the age of reptiles ; " and the fact that the few yet 

 found are at all comparable with such specialised forms as still 

 exist, must convince us, that we shall have to seek far beyond 

 even the earliest of these remains, for the first appearance of the 

 mammalian type of vertebrata. 



Extinct Birds. 



Compared with those of mammalia, the remains of birds are 

 exceedingly scarce in Europe and America ; and from the wander- 

 in" habits of so many of this class, they are of much less value 



