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 
Dromatherium already noticed, from North America. They 
have been 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- 
ing habits of so many of this class, they are of much less value 
