INTRODUCTION, XV 
bones and teeth should have escaped notice ; especially 
when the remains of the Cetiosauri and other Reptilian 
inhabitants of those ancient seas are so abundant. 
From the remote period in which the remains of Mam- 
mals first make their appearance, to that in which we 
again get indubitable evidence of their existence, a lapse 
of time incalculably vast has occurred. We trace it 
by the successive deposition from seas and estuaries, of 
enormous masses of rocks of various kinds, the grave- 
yards of as various extinct forms of animal and vege- 
table life. The shelly limestone of Stonesfield, which 
contains the bones of the Amphitheria and Phascolo- 
theria, lies upon Inferior Oolite. Upen it have been 
accumulated the strata of the Great Oolite, the Corn- 
brash and the Forest Marble; and upon these have been 
successively piled the Oxford group of Clay,* Calcareous 
Grit and Coral Rag, the Kimmeridge Clay and Portland 
Stone. In the extensive range of Wealden Rocks, de- 
posited after the formation of the Portland Sands by the 
waters of an immense estuary, and rising to the height 
of eight hundred feet, no true indications of warm- 
blooded animals have been hitherto discovered.t Four 
hundred feet deep of Gault and Greensand rest upon the 
Wealden, but reveal no trace of Cetacean or other form of 
Mammalian life. 
* The fossil in the Woodwardian Museum, referred to at p. 520, gives the 
sole indication of a marine mammal at this period. Although the circumstances 
of its discovery are far from being satisfactory, I am unwilling to lose sight of 
this indication, because the cervical vertebra, whilst they evince by their extreme 
compression and anchylosis, the cetacean characters, present well-marked specific 
distinctions from all known recent or fossil species. 
+ Lyell, ‘ Elements of Geology,’ 8yo. 1838, p. 345 ; Fitton, ‘Geology of 
Hastings,’ p. 58 ; and, especially, Mantell, ‘Geology of Sussex,’ 4to. 1622. and 
subsequent Works of this original and successful explorer of the Wealden. 
+ See my paper in the ‘Proceedings of the Geological Society,’ Dec. 17th, 1845, 
“ On the supposed Bones of Wading Birds from the Wealden.” 
