Page:Popular Science Monthly Volume 3.djvu/475

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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."

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