THE BASIN AND BED OF THE ATLANTIC. 311 



-cliiiiery suggests that the streams of running water in the sea play 

 The causes that pro- rather about its sui'face than in its depths ; that 

 duce currents in the f^Q causes which procluce curreuts reside at and 



sea reside near its i /> i i t • i 



surface. near the surface ; that these causes are changmg heat 



and alternating cold ^vith theu' powers of contraction and expansion 

 — winds and sea-shells ^^dth evaporation and precipitation ; and it 

 is certain that none of these agents appear capable of reachmg 

 with their influences very far down into the depths of the great and 

 wide sea. They go not much, if any, farther do^\Ti than the 

 light can reach. On the other hand, the most powerful agents in 

 the atmosphere reside at and near its bottom ; so that, where these 

 two great oceans meet — the aqueous and the aerial — there we 

 probably have the greatest conflict and the most powerful display 

 •of the forces that set and keep them in motion, making them to 

 rage and roar. 



601. The greatest depth at wliich running water is to be found 

 Their depth, in the sea is probably in the narrowest part of 



the Gulf Stream, as, coming from its mighty fountain, it issues 

 through the Florida Pass. The deep-sea thermometer shows that 

 even here there is a layer of cold water in the depths beneath, so 

 that this " river in the sea " may chafe not against the solid bottom. 

 What revelations of the telescope, what wonders of the microscope, 

 what fact relating to the physical economy of tliis terrestrial globe, 

 is more beautiful or suggestive than some of the secrets wliich have 

 been fished up from the caverns of the deep, and brought to light 

 from the liidden paths of the sea ? ^ 



602. In my researches I have as yet found no marks of running 

 The cushion of still water impressed upon the foundations of the sea 

 n^s. "^ ^ ' '^ " beyond the depth of two or three thousand feet. 

 Should future deep-sea soundings establish this as a fact in other 

 seas also, it will prove of the greatest value to submarine telegraphy. 

 What may be the thickness of this cushion of still water that covers 

 the bottom of the deep sea is a question of high interest, but we 

 must leave it for future mvestigation. 



603. In Chapter X. (The Salts of the Sea), I have endeavoured 

 The conservators of to show how soa-shells and marine uisects may, by 



^''^** ^^ - reason of the ofiices which they perform, be regarded 

 as compensations in that exquisite system of physical machinery 

 by which the harmonies of nature are preserved. But the trea- 

 sures of the lead and revelations of the microscope present the 

 insects of the sea in a new and stiU more striking light . We 



