< Page:Popular Science Monthly Volume 3.djvu
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THE PROBLEMS OF THE DEEP SEA.
Apiocrinidæ, an order hitherto regarded as extinct, which attained its maximum in the Pear Encrinites of the Jurassic period, and whose latest representative hitherto known was the Bourguettocrinus of the chalk. Some years previously, Mr. Absjörnsen, dredging in 200 fathoms in the Hardangerfjord, procured several examples of a star-tish (Brisinga), which seems to find its nearest ally in the fossil genus Protaster. These observations place it beyond a doubt that animal life is abundant in the ocean at depths varying from 200 to 300 fathoms, that the forms at these great depths differ greatly from those met with in ordinary dredgings, and that, at all events, in some cases, these animals are closely allied to, and would seem to be directly descended from, the Fauna of the early tertiaries.
"I think the latter result might almost have been anticipated; and, probably, further investigation will largely add to this class of data, and will give us an opportunity of testing our determinations of the zoological position of some fossil types by an examination of the soft parts of their recent representatives. The main cause of the destruction, the migration, and the extreme modification of animal types, appears to be change of climate, chiefly depending upon oscillations of the earth's crust. These oscillations do not appear to have ranged, in the northern portion of the Northern Hemisphere, much beyond 1,000 feet since the commencement of the Tertiary epoch. The temperature of deep waters seems to be constant for all latitudes at 39°, so that an immense area of the North Atlantic must have its conditions unaffected by tertiary or post-tertiary oscillations."[1]

As we shall see, the assumption that the temperature of the deep sea is everywhere 39° Fahr. (4° Cent.) is an error, which Dr. Wyville Thomson adopted from eminent physical writers; but the general justice of the reasoning is not affected by this circumstance, and Dr. Thomson's expectation has been, to some extent, already verified. Thus, besides Globigerina, there are eighteen species of deep-sea Foraminifera identical with species found in the chalk.

Embedded in the chalky mud of the deep sea, in many localities, are innumerable cup-shaped sponges, provided with six-rayed silicious spicula, so disposed that the wall of the cup is formed of a lace-work of flinty thread. Not less abundant, in some parts of the chalk formation, are the fossils known as Ventriculites, well described by Dr. Thomson as "elegant vases or cups, with branching, root-like bases, or groups of regularly or irregularly spreading tubes delicately fretted on the surface with an impressed net-work like the finest lace;" and, he adds: "When we compare such recent forms as Aphrocallistes, Iphiteon, Holtenia, and Askonema, with certain series of the chalk Ventriculites, there cannot be the slightest doubt that they belong to the same family—in some cases to very nearly-allied genera."[2]

Prof. Duncan finds "several corals from the coast of Portugal more nearly allied to chalk-forms than to any others."

The stalked crinoids, or feather-stars, so abundant in ancient times, are now exclusively confined to the deep sea, and the late explorations

  1. ↑ "The Depths of the Sea," pp. 51, 52.
  2. ↑ Ibid., p. 484.
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