THE MUSEUM. 



7i 



nental slopes the conditions are often 

 very favorable to marine life. Cur- 

 rents of comparatively warm water, 

 like the Gulf Stream, sweep along 

 bringing fresh pure water and supplies 

 of food to the animals along their 

 track. The differences between the 

 abysses and the slopes is rather a mat- 

 ter of temperature than of mere depth. 

 But the temperature itself is some- 

 what dependent on the depth, the in- 

 fluences of the great warm currents 

 rarely extending below seven or eight 

 hundred fathoms and this depth cor- 

 responds roughly to a temperature of 

 about forty degiees Fahrenheit. Be- 

 low this it diminishes as the depth in- 

 creases, at the rate of about one- 

 tenth of a degree to one hundred fath- 

 oms until the freezing point is reach- 

 ed, though there is no reason to sup- 

 pose that the abyssal water ever act- 

 ually becomes cangealed. 



To this cold dark area of the ocean 

 bottom has been applied the name of 

 the Benthal or Abyssal region. 



To the region, chiefly on the conti- 

 dental slopes, between the Litoral and 

 Abyssal regions, I gave some years 

 ago the name of the Archibenthal Re- 

 gion. 



These divisions have been recogniz- 

 ed by various writers and have had 

 several terms applied to them. Those 

 I have mentioned seem to me as char- 

 acteristic as any, and in some respects 

 more convenient than any I have 

 heard used. 



Let us now consider the conditions 

 under which life exists in the Abyssal 

 and Archibenthal regions. It may be 

 premised that the differences between 

 them are largely of degree and not of 

 kind and do not require that the two 

 regions should be considered separate- 



The chief characteristics reside in 

 the composition of the sea water, in- 

 cluding its contained gases; in the dy- 

 namic status of the deeps, especially 

 in relation to temperature and press- 

 ure; in the mechanical qualities of the 

 materials of which the oceanic floor is 



composed; and lastly, in the food sup- 

 ply- 



As determined by physicists and 

 chemists the water of the deep sea 

 varies in the properties of natural salts, 

 carbonic acid and air contained in it 

 very much as does the surface water. 

 In general at the surface the wanner 

 water of the tropics has the more salt 

 and the less nitrogen. When carried 

 by currents to the Polar regions and 

 cooled, this tropical water sinks to the 

 bottom carrying its excess of salt 

 along with it. The Polar waters are 

 less saline and contain more nitrogen. 

 The proportion of atmospheric air in 

 the water is found strictly related to 

 the temperature, the pressure at great 

 depths being regarded as having no 

 bea-ing on the question. The amount 

 of oxygen in the sea water diminishes 

 gradually as we descend from the sur- 

 face until about 359 fathoms is reach- 

 ed, when it ceases to change or at 

 most increases slightly until the bot- 

 tom is attained 



Carbonic acid, according to Tornoe, 

 does not exist in a free state in sea 

 water, but only in the form of carbon- 

 ates or to a less degree of bicarbon- 

 ates. Unless the decomDOsition of 

 animal matter in some manner sets 

 free the carbonic acid, this conclusion 

 is one which cannot be adopted with- 

 out question, especially when we con- 

 sider the great difficulties which are 

 encountered in any attempt to obtain, 

 or when obtained to analyze abyssal 

 water. . The effect of erosion on the 

 shells dredged, from the deeps, even 

 when they contain the living animal, 

 is so strongly marked, the devices for 

 protection against erosion are so rec- 

 ognizable in various species, that the 

 biologist may well call the physicist to 

 a halt, while the latter re-examines 

 his data. It is certain that erosive 

 agencies, of which the effects are in- 

 distinguishable from those known to 

 be due to carbonic acid in other in- 

 stances, are extremely active in the 

 deeps. 



In general it seems as if we might 



