the years 1868, 1869, and 1870," says Dr. Wyville Thomson, "fifty-seven
hauls of the dredge were taken in the Atlantic at depths beyond 500
fathoms, and sixteen at depths beyond 1,000 fathoms, and, in all cases,
life was abundant. In 1869, we took two casts in depths greater than
2,000 fathoms. In both of these life was abundant; and with the deepest
cast, 2,435 fathoms, off the month of the Bay of Biscay, we took living,
well-marked and characteristic examples of all the five invertebrate sub-
kingdoms. And thus the question of the existence of abundant animal life
at the bottom of the sea has been finally settled and for all depths, for
there is no reason to suppose that the depth anywhere exceeds between
three and four thousand fathoms; and if there be nothing in the
conditions of a depth of 2,500 fathoms to prevent the full development of
a varied Fauna, it is impossible to suppose that even an additional
thousand fathoms would make any great difference."[5]

[Footnote 5: _The Depths of the Sea_, p. 30. Results of a similar kind,
obtained by previous observers, are stated at length in the sixth
chapter, pp. 267-280. The dredgings carried out by Count Pourtales, under
the authority of Professor Peirce, the Superintendent of the United
States Coast Survey, in the years 1867, 1868, and 1869, are particularly
noteworthy, and it is probably not too much to say, in the words of
Professor Agassiz, "that we owe to the coast survey the first broad and
comprehensive basis for an exploration of the sea bottom on a large
scale, opening a new era in zoological and geological research."]

As Dr. Wyville Thomson's recent letter, cited above, shows, the use of
the trawl, at great depths, has brought to light a still greater
diversity of life. Fishes came up from a depth of 600 to more than 1,000
fathoms, all in a peculiar condition from the expansion of the air
contained in their bodies. On their relief from the extreme pressure,