90 



ISLAND LIFE. 



[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.^ 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 w^arm 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." ^ 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 MicroscopicalJournal, Yo\. XIX., 

 New Series, p. 84. 



^ Proceedings of the Royal Society^ Vol. XXIV. p. 632. 



