THE DEEP SEA AND ITS CONTENTS. .331 



satisfaction of finding myself supported by Mr. H. B. Brady, into 

 whose most competent charge the Foraminifera of the Challenger 

 have been given for " working up." For the result of a series of 

 most careful comparisons between the Globigerinas brought up 

 from any bottom and those captured floating in the upper waters 

 of the same region, shows that the shells of the former so greatly 

 exceed those of the latter in size and massiveness as to make it 

 certain that they continued to live and grow after their subsidence. 



The careful examination in which Mr. Murray has been en- 

 gaged of the calcareous deposits (resembling chalk in process of 

 formation), chiefly consisting of globigerina-ooze, but also con- 

 taining the disintegrated remains of free-swimming Pteropod mol- 

 luscs, as well as of shells and corals that have lived on the bottom, 

 has led him to the remarkable conclusion that in their descent 

 from the upper waters towards the deeper sea-bottoms the thin 

 shells of the Globigerinas and the yet more delicate pteropod 

 shells are again dissolved, by the agency of the carbonic acid 

 that is held in larger proportion in those abyssal waters. And 

 thus it was that on the deepest parts of the Oceanic area, though 

 Globigerince were captured by the tow-net in the same abundance 

 as elsewhere, their remains were entirely wanting on the bottom 

 beneath. At intermediate depths the ooze and the red clay 

 would often be found mixed, in proportions that seemed related 

 to the depth. But in the shallower waters not sufficiently charged 

 with carbonic acid to exert any solvent powers, the organic de- 

 posit prevailed almost to the exclusion of the inorganic. This, 

 then, seems to have been the condition of the marine area in 

 which the old Chalk was deposited ; a variety of considerations 

 pointing to the conclusion that the sea-bottom whereon accumu- 

 lated the foraminiferal ooze of which it is almost entirely composed, 

 was of no considerable depth. 



But the surface-waters are also inhabited by microscopic 

 organisms whose skeletons are composed, not of carbonate of 

 lime, but of silex ; and of these, some — the Diatoms — are vege- 

 table, whilst others — the Radiolarians — are animals of about the 

 same simplicity as the Foraminifera. The Diatoms abound in 

 those colder seas which are not prolific in Foraminifera; often 

 accumulating in such numbers as to form green bands that attract 

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