90 
ISLAND LTFE. 
[part i. 
Mr. H. B. Brady has led him to a different conclusion ; for he 
finds numerous forms at the bottom quite distinct from those 
which inhabit the surface, while, when the same species live 
both at surface and bottom, the latter are always larger and 
have thicker and stronger cell-walls. This view is also sup- 
ported by the fact that in many stations not far from our own 
shores Globigerinse are abundant in bottom dredgings, but are 
never found on the surface in the towing-nets. 1 These organisms 
then exist almost universally where the waters are pure and are 
not too cold, and they would naturally abound most where the 
diffusion of carbonate of lime both in suspension and solution 
afforded them an abundant supply of material for their shelly 
coverings. Dr. Wallich believes that they flourish best where 
the warm waters of the Gulf Stream bring organic matter from 
which they derive nutriment, since they are wholly wanting 
in the course of the Arctic current between Greenland and 
Labrador. Dr. Carpenter also assures us that they are rigorously 
limited to warm areas. 
Now with regard to the depth at which our chalk was formed, 
we have evidence of several distinct kinds to show that it was 
not profoundly oceanic. Mr. J. Murray, in the Report already 
referred to, says: “The Globigerina-oozes which we get in 
shallow water resemble the chalk much more than those in 
deeper water, say over 1,000 fathoms.” 2 This is important and 
weighty evidence, and it is supported in a striking manner by 
the nature of the molluscan fauna of the chalk. Mr. Gwyn 
Jeffries, one of our greatest authorities on shells, who has 
himself dredged largely both in deep and shallow water and 
who has no theory to support, has carefully examined this 
question. Taking the whole series of genera which are found 
in the Chalk formation, seventy-one in number, he declares 
that they are all comparatively shallow-water forms, many 
living at depths not exceeding 40 to 50 fathoms, while some 
are confined to still shallower waters. Even more important 
is the fact that the genera especially characteristic of the deep 
1 Notes on Reticularian Rhizopoda ; in Microscopical Journal, Vol. XIX., 
New Series, p. 84. 
3 Proceedings of the Royal Society, Vol. XXIV. p. 532. 
