344 . 
THE CRETACEOUS EPOCH. 
division of zoopliytes is not known to exist in low 
latitudes, in our modern seas. * The cretaceous 
strata of the chalk, with their nodules and veins of 
flint, have more the character of a chemical pro- 
duction, than of a mere mechanical deposit ; and 
may perhaps owe their origin to precipitation from 
thermal waters. The shells and crustaceous co- 
verings of the echini are invariably changed into 
calcareous spar ; and in many instances the tere- 
bratulcenYe. twisted and contorted in every direction, 
without the shells exhibiting a single fracture ; 
changes which probably resulted from the influence 
of a high temperature under considerable pressure. 
With the exception of the pentacrinus, tlie teeth 
of fishes resembling those of the shark, the teeth 
of crocodiles, and perhaps a few shells t, the organic 
remains of the chalk differ entirely from all known 
existing species, as well as from the fossils of other 
formations. The thickness of the chalk, which is 
estimated at upwards of 1200 feet, and the immense 
variety and numbers of its organic remains, evince 
that the agents which produced it were in full 
activity through a long period of time.t Although 
* M. Lamouroux observes, that in the colder latitudes the Cellarias, 
and Sertulariae alone are to be found ; with a few closely woven sponges, 
and a small number of alcyonia. The minute Penlatrimis Eiirojjccus, 
recently discovered by Mr. Thompson in the Cove of Cork, is an 
exception ; but the recent Pentacrimis Caput Mcdusce, to which the 
pentacrinal stems that occur in the chalk bear considerable analogy, 
is found in the sea off the West India Islands. 
f Even these few exceptions are very equivocal, and probably the 
species will hereafter prove to be distinct from their supposed ana- 
logues. 
1 The fossils of the chalk of Sussex are enumerated in the Catalogue 
in the Appendix to this work. In the list of the organic remains of 
