THE PERMANENCE OF CONTINENTS. 
121 
that ‘this chalk consists simply of comminuted corals and shells 
of the reef,’ and is, when examined microscopically, ‘ found to 
be destitute of the minute organisms abounding in the chalk of 
England/ Mr. Wallace states that in several growing reefs a 
similar formation of modern chalk, undistinguishable from the 
ancient, has been observed. 
Mr. Wallace thus assumes that the Chalk is derived from 
excessively fine mud produced by the decomposition and denu- 
dation of coral reefs ; but this view appears to me to be 
untenable. Mr. Murray expressly states that no Globig evince 
were found in any of the enclosed seas of the Pacific which 
possess this chalky bottom ; and to account for Globigerina in 
the Chalk it has to be supposed that the Chalk sea was open to 
the Gulf Stream, i.e. the Atlantic. Further, to provide the 
necessary conditions we are obliged to suppose this vast sea to 
have been bordered with islands and coral reefs, and that no 
large rivers flowed into it, and yet absolutely no traces of these 
coral reefs remain, while an inland sea could hardly have 
existed in proximity to a great permanent continent without 
some rivers draining into it. A curious piece of reasoning is 
that in the Maestricht and Faxoe chalks ‘ we have a clear indi- 
cation of the source whence the white calcareous mud was 
derived which forms the basis of the chalk/ If these local 
and far newer deposits are seen to be highly coralline and the 
Chalk is not seen to be so, we have rather a clear indication 
that they were not deposited under the same conditions. The 
presence of Mosasaums in the Maestricht beds, and the far newer 
aspect of its fauna, show that it must have belonged to an 
altogether different period, probably the one represented in 
America by a great so-called Cretaceous series containing a 
mixture of Cretaceous and Tertiary mollusca, dicotyledonous 
plants, and Mosasaurus. From every point of view, in fact, 
the inference that the vast Cretaceous deposits are analogous to 
small local deposits of coral mud in the Pacific does not appear 
to be the true one. 
With regard to the probable depth of the ocean which 
deposited the Chalk, the evidence brought together by Mr. 
Wallace is less unsatisfactory. Mr. J. Murray, for instance, 
sees the greatest resemblance to it in mud from depths of less 
than 1000 fathoms ; and Dr. Gwyn Jeffreys finds that all the 
Mollusca of the Chalk are comparatively shallow- water forms. 
We must bear in mind, however, that the characteristically 
deep-sea families and genera, such as Bulla and the Solenocon- 
chia, Leda, JSfeoera, and Verticordia, would have long since been 
dissolved away if present ; while great and highly characteristic 
cretaceous genera, such as Inoceramus and HippuriteSy are wholly 
