MUSEUM OF COMPARATIVE ZOOLOGY. 367 



it entirely fades away. As we have already seen, this is not the case, 

 and Captain McAndrew has himself lately helped to dispel the illusion. 

 Nevertheless, it is true that a change is perceptible in the character 

 and size of animals inhabiting respectively deeper and deeper waters, 

 as compared with those of the shallow coast zone. It may very justly 

 be said that we have in the sea something corresponding to the alpine 

 and subalpine flora, when contrasting higher levels with the plains ; 

 only that our submarine deep-water flora, or rather fauna, consists 

 mostly of creatures hitherto little known, or even entirely unknown. 



It is a surprising fact that the variety of marine plants does not keep 

 pace with the variety of animals ; they make a poor show when com- 

 pared with the many and diversified sea-weeds found in the littoral 

 mud-flats and upon shoal rocky bottoms. The sponges, however, thrive 

 in deep waters better than the ordinary algoe ; but the large and val- 

 uable sponges now gathered in such quantity along the whole coast 

 of Florida are found on the littoral shoals only. In deep water we 

 find, with a variety of larger species, a great number of small species 

 of the same type, and among them a diminutive Hyalonema. 



Permit me a suggestion here. You have repeatedly commemorated 

 the discovery, by officers of the Coast Survey, of some submarine ledge 

 or ridge, or peculiar configuration of the sea-bottom, by associating 

 their names with the field of their operations. It would be appropriate 

 and just that this extensive coral plateau, the characteristic fauna of 

 which M. Pourtales has so faithfully explored, should bear his na^ie and 

 be called the " Pourtales Plateau." 



To the seaward of this coral table-land, the bottom sinks rapidly to 

 a depth of four or five hundred fathoms, reaching even eight hundred 

 fathoms and more, though our successive dredgings have hardly ex- 

 tended beyond seven hundred fathoms. Over the whole of this area, 

 which properly constitutes the lower floor of the Gulf Stream, the 

 sea-bottom presents a uniform accumulation of thick, adhesive mud,* 

 in which animal life is much less profuse than upon the coral plateau. 

 It cannot, however, be assumed that this diminution of life is owing 



* When dried, this deep-sea mud, with its innumerable and characteristic Forami- 

 nifera, remarkably resembles the chalk-marls of the cretaceous formation. The green- 

 sand formation I have not investigated myself, but it has been minutely studied by Mr. 

 Pourtales, who has ascertained that it is the result of a peculiar alteration, disintegra- 

 tion, and final aggregation of Foraminifera. 



