146 THREE CRUISES OF THE " BLAKE." 



fly sell, which forms so important a part in the geology of south- 

 ern Euroj^e, he thinks must have been a deep water deposit. 

 The beds of the mesozoic period in which ammonites are found, 

 Fuchs looks upon as deep-water formations, because in all dis- 

 tinctly shallow-water beds of that time no ammonites have been 

 found. 



From the time of the earliest examination of the globigerina 

 mud of the Atlantic, by Bailey and Ehrenberg, that deposit has 

 been compared to the chalk ; and since the time of deep-sea 

 investigations, the white chalk, with its globigerinse, Hexactinel- 

 lidse, and peculiar echinoderms, has always been regarded as an 

 antique type of deep-sea deposits. Jeffreys, on the contrary, 

 assumes it to be a shallow-water formation from the study of 

 the moUusks. His reasons are that the foraminifera of the 

 chalk are many of them pelagic, and might therefore be found 

 in littoral or shallow-water deposits ; that globigerina ooze con- 

 tains a large percentage of silica, Avhile the chalk is nearly pure 

 carbonate of lime ; that the mollusca of the chalk are all litto- 

 ral types ; and that the so-called deep-sea genera are wanting. 

 Yet we find in the chalk such genera as Terebratula, Lima, 

 Pecten, and Spondylus, all of which are found in very deep 

 water, — to a depth of fourteen hundred and fifty fathoms. 

 While admitting that pelagic foraminifera frequently occur in 

 littoral deposits, it seems impossible that some of the beds of 

 foraminifera of great thickness should have been deposited oth- 

 erwise than in deep water. Foraminifera ought to serve as 

 excellent guides in identifying deep-sea formations, since genera 

 like Cristellaria, Marginulina, Clavulina, Nodosaria, and others, 

 with arenaceous -and siliceous tests, occur in the seas of to-day, 

 principally in deeper waters. 



The present chemical constitution of the chalk is also not the 

 one in which it was deposited, the siliceous particles having 

 probably been concentrated as flint. As regards the fauna, 

 the mollusks are not so good a guide as either the sponges or 

 the echini, the representatives of both of which — Hexactinel- 

 lidse, Ananchytidse, Pourtalesise, Salenise, and Echinothuriae — 

 are eminently deep-sea types. That many of the molluscan 

 forms which lived in the chalk have been dissolved as arago- 



