146 THREE CRUISES OF THE “ BLAKE.” 
flysch, which forms so important a part in the geology of south- 
ern Europe, 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 globigerinze, Hexactinel- 
lidæ, 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 mollusks. 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, while the chalk 1s 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- 
lide, Ananchytid:e, Pourtalesiæ, Saleniæ, and Echinothurie — 
are eminently deep-sea types. That many of the molluscan 
forms which lived in the chalk have been dissolved as arago- 
