168 THREE CRUISES OF THE “ BLAKE." 
A careful study of the facies, of the mode of occurrence of 
deep-sea faunz, and of the nature of the bottom as developed 
by recent explorations, will assist us in obtaining a clearer idea 
of the conditions under which the continental and abyssal de- 
posits of past ages, dependent not only on the depth, but on 
the character of the bottom, have been made. The existence 
of the same species at points remote from one another appear 
to indicate a somewhat uniform fauna in deep water, extend- 
ing perhaps, with slight modifications, over extensive areas, from 
the arctic to the antarctic in both the Atlantic and Pacific 
oceans. Yet the localization of certain species was one of the 
most characteristic results of the earlier dredging explorations, 
and extremely rare animals came up in the dredge by hundreds 
in certain localities. 
The thousands of specimens of some of the species of echino- 
derms, crustacea, polyps, and other invertebrates, which have 
been dredged from favorable localities, give us an example of 
the localization of species identical with that found in many fos- 
siliferous beds of former geological periods. The wide geo- 
graphical distribution of other species has been equally well 
proved from their occurrence both in the shallow waters of the 
arctic region and in deep water in more southern latitudes, but 
of course this distribution is dependent to a great degree upon 
the character of the bottom. 
Some fishes only extend to a depth of five hundred fathoms ; 
others take their greatest development below that belt, and many 
of them are blind. Below five hundred fathoms we have a large 
number of Gadoids, Macruroids, Ophidiidz, and fishes with 
large eyes, slender bodies, and rudimentary skeletons. Echino- 
derms live in masses at considerable depths, and form huge 
banks, containing a great variety of forms, similar to those 
found in some of the favored localities for fossils in New York 
and Iowa. 
Species of Echinus, of Brissopsis, of Periaster, of Ophi- 
oglypha, of Ophiomusium, and of Ophiozona have been brought 
up in countless numbers in the dredge. Pentacrinus forms to- 
day, as it did in the jurassic seas, forests of specimens at a depth 
of one hundred to one hundred and fifty fathoms. Deep-sea 
