511 
conifers, with their roots still attached to them, are preserved. 
Yet, when the geologist inquires if any land animals, of a higher 
grade than reptiles, lived during any one of these three periods, the 
rocks arc all silent, save one thin layer, a few inches in thickness, 
and this single page of the earth’s history has suddenly revealed to 
us in a few weeks, the memorials of so many species of fossil 
mammalia, that they already out-number those of many a sub- 
division of the Tertiary series, and far surpass those of all the 
other Secondary rocks put together ! " 
Following the upper Oolitic series, we come to the Wealden beds, 
which according to Sir Charles I. yell are, in England, the remains of 
an ancient delta, but, in Mr. S. Y. Wood, .Jun.’s, opinion, the bed of 
a large fresh-water lake, which was contiguous to the sea. In these 
fresh-water deposits we might naturally expect to find the remains of 
mammalia, but no Wealden mam miter is at present known. 
The middle and upper Xeocomian strata are in like manner, as 
far as our present knowledge goes, non-mammaliferous, and so are 
the Cretaceous beds. 
Although the remains of Secondary mammals are thus so few in 
number, there is no reason to suppose that mammalian life was of 
rare occurrence during the Mesozoic era. The ten specimens from 
the Stonesfield slate belong to four different species, while those 
from the Purbeck dirt-bed have been referred to fourteen, including 
insectivorous, carnivorous, and herbivorous forms. I am not aware 
that with the exception of the two minute teeth found at Stuttgart, 
and two lower jaws of a small mammal ( Dromatherium) from the 
Triassic coal beds of North Carolina, in the United States,* any 
Secondary mammalian fossil has been found out of the British 
Isles. All the remains at present known to us of the mammals 
which may have existed over the whole world, previous to the 
commencement of the Eocene period, might be packed in a good- 
sized cigar box ! 
But the best illustration which geology affords of the imperfection 
* Since the above was written, I have learned that the remains of a small 
marsupial ( Dryolestes prisons) have been discovered by Professor Marsh, in 
the Jurassic rocks of the United States. 
