1868;] 



on Deep-sea Dredgings. 



199 



ocean at depths varying from 200 to 800 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 ; an probably 

 further investigation will add largely to this class of data, and will give us an 

 opportunity of testing our determination 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 oscilla- 

 tions of the earth's crust. These oscillations do not appear to have ranged, in 

 the northern portion of the Northern Hemisphere, much beyond 1000 feet since 

 the commencement of the Tertiary epoch. The temperature of deep water 

 seems to be constant for all latitudes at 39° ; so that an immense area of the 

 North Atlantic must have had its conditions unaffected by Tertiary or Post-ter- 

 tiary oscillations. 



One or two other questions of the highest scientific interest are to be solved 

 by the proposed investigations : — 



1st. The effect of pressure upon Animal life at great depths. There is great 

 misapprehension on this point. Probably a perfectly equal pressure to any 

 amount would have little or no effect. Air being highly compressible, and 

 water compressible only to a very slight degree, it is probable that under a pres- 

 sure of 200 atmospheres, water may be even more aerated, and in that respect 

 more capable of supporting life, than at the surface. 



2nd. The effect of the great diminution of the stimulus of Light. From the 

 condition of the Cave Fauna, this latter agent probably affects only the deve- 

 lopment of colour and of the organs of sight. 



I have little doubt that it is quite practicable, with a small heavy dredge, 

 and a couple of miles of stout Manilla rope, to dredge at a depth of 1000 

 fathoms. Such an undertaking would, however, owing to the distance, and the 

 labour involved, be quite beyond the reach of private enterprise. What I am 

 therefore anxious for is, that the Admiralty may be induced, perhaps at the in- 

 stance of the Council of the Royal Society, to send a vessel (such as one of 

 those which accompanied the Cable Expedition to take soundings) to carry out 

 the research. I should be ready to go any time after July ; and if you would 

 take part in the investigation, I cannot but believe that it would give good results. 



I would propose to start from Aberdeen, and to go first to the Rockall fish- 

 ing-banks, where the depth is moderate, and thence north-westward, towards 

 the coast of Greenland, rather to the north of Cape Farewell. We should thus 

 keep pretty nearly along the isotherm of 39°, shortly reaching 1000 fathoms 

 depth, where, allowing 1000 feet for oscillations in level, and 1000 feet for in- 

 fluence of surface- currents, summer heat, &c, we should still have 4000 feet of 

 water whose conditions have probably not varied greatly since the commence- 

 ment of the Eocene epoch. 



Yours most truly, 



Wyville Thomson. 



These letters having been considered, it was 

 Resolved, — That the proposal of Drs. Carpenter and Wyville Thomson be ap- 

 proved, and recommended to the favourable consideration of the authorities of 



