THE PROBLEMS OF THE DEEP SEA. 461 



Apiocrinidm, an order hitherto regarded as extinct, which attained its maximum 

 in the Pear Eucrinites of the Jurassic period, and whose latest representative 

 hitherto known was the Bourguettocrinus of the chalk. Some years previously, 

 Mr. Absjornsen, dredging in 200 fathoms in the HaiC^gerfjord, procured sev- 

 eral 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 or- 

 dinary 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, prob- 

 ably, 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 representa- 

 tives. 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." l 



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 forma- 

 tion, 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 Ashonema, 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. a Ibid., p. 484. 



