92 ISLAN-D LIFE 



both at the surface, at various depths in the water, and at 

 the bottom. It was long thought that they were surface- 

 dwellers only, and that their dead tests sank to the bottom, 

 producing the Globigerina-ooze in those areas where other 

 deposits were absent or scanty. But the examination of 

 the whole of the dredgings and surface-gatherings of the 

 Challenger by 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 supported 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 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 ; but Mr. Brady says that a dwarf variety of Globi- 

 gerina was found in the soundings of the North Polar 

 Expedition in Lat. 83° 19' N. 



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. Dr. Gwyn Jeffreys, one of our greatest 



^ Notes on Reticularian Rhizopoda ; in MicroscopicalJoumalj Vol. XIX., 

 New Series, p. 84. 



2 Proceedings of the Royal Society ^ Vol. XXIY. p. 532. 



