284 THE ATLANTIC. [chap. v. 



much reason for believing that the great ocean depressions of 

 the present time have persisted through all the later geological 

 periods, back probably as far as the Permian Age, and perhaps 

 much farther. If this be so, the length of time during which 

 the vast area occupied by the abyssal fauna has maintained its 

 continuity, and probably a great uniformity in essential condi- 

 tions, is incalculable ; that is to say, it can not, in the present 

 state of our knowledge, be reduced even approximately to as- 

 tronomical time. 



In discussing the general distribution of temperature, the 

 reasons have been already given which have led us to the be- 

 lief that there is a constant underflow of water from the south 

 northward, and one would naturally expect some indication of 

 migration having proceeded, and continuing to proceed, in that 

 direction. It is impossible to come to a definite conclusion 

 on this question until tlie species in the different groups shall 

 have been critically determined : there seems, however, to be 

 little doubt that the families which are specially characteris- 

 tic of the abyssal fauna, such as the Hexactinellid sponges, 

 the stalked Crinoids, the Echinothuridse, and the genera al- 

 lied to Infulaster and Micraster among the Echinidea, are 

 more abundant, and larger and more fully developed, in the 

 Antarctic Ocean, and in the great ocean of the water hemi- 

 sphere generally, than they are in the Atlantic and the North 

 Pacific. 



Our preliminary dredgings in the North Atlantic along the 

 coasts of Portugal and Spain were chiefly on the globigerina 

 ooze at depths under 2000 fathoms ; and there we found all 

 the ordinary forms of deep-sea life abundant, particularly 

 sponges referable to the genera Ilyalonema, Aphrocallistes, 

 Euplectella, Corallistes, and Caminus. As this area had been 

 gone over by Mr. Gwyn Jeffreys in the Porcupine we were 

 already aware that stalked crinoids and corals of Tertiary types 

 occurred. 



