the relative Age of Tertiary Deposits. 535 
servation of their remains. ‘The only bones of frequent oc- 
currence are those placed within the cavity of the tympanum, 
and which being of a more solid texture than the rest of the 
skeleton are found in a very perfect state. These bones belong 
to an unknown genus, and are peculiar to this part of the crag 
formation. Teeth of cartilaginous species are occasionally met 
with, but in the course of my own researches I have never suc~ 
ceeded in obtaining them. 
The ocean, however, which deposited the red crag was one 
evidently swarming with fish; and their mineralized remains, 
generally consisting of the teeth and portions of the palate, 
are preserved in great abundance. Among them are the ge- 
nera Carcharias, Myliobates, Galeus, Lamna, Notidanus, and 
Platax, &c. Wherever this deposit is detected, some of 
these genera invariably accompany it. Itis here also that we 
first meet with the higher orders of the animal kingdom. The 
teeth of the Mastodon, Elephant, Hippopotamus, and other 
Mammalia are deposited with the Mollusca of this period, and 
in addition to them I may mentioned the bones of Birds, which 
I have recently obtained from several localities. 
Turning from the groups of vertebrated animals to those 
of the Radiata, we naturally revert to that extensive assem- 
blage of Polypifera which characterize so large a portion of 
the coralline crag, and to which nothing analogous is pre- 
sented by any other tertiary deposit in this island. ‘The 
Echinide too, so sparingly distributed in the London clay 
and upper beds of the crag, are here met with in compa- 
rative abundance; fragments and spines are of constant oc- 
currence, and some of the more perfect specimens which have 
been obtained exhibit the most elegant forms, and are widely 
removed from known species. ‘There are one or two spots 
in the red crag where Echini have congregated in myriads, 
but the species approximate more nearly to those now exist- 
ing, and with which they may perhaps be identified. The com- 
parison of the Crustacea from the two beds has furnished a 
corresponding result; but the remains of this group are spa- 
ringly met with, and generally in an unfavourable state for ex- 
amination. 
I now proceed to notice that class which among organized 
beings are thought to furnish the geologist with the most im- 
portant data in his investigation of tertiary formations, and to 
which he especially directs his attention when fossiliferous 
strata of different periods are superposed in the same area, or 
when he is desirous of ascertaining the probable epoch to 
which an isolated deposit should be referred. 
Mr. Searles V. Wood, who possesses the largest series extant 
