GEOLOGY. 251 



25 and 35 W., this. successively increases by evaporation to-}- 17.3 

 and -j- 20.8. On the same longitude, at lat. 15 S., the saltness is 

 -{- 31.5, lat. 12-14 N.-j- 21.9 and 19.4 ; thus the current is less salt 

 than the ocean near it indicating the freshening influence of the 

 great rivers of Guinea. Near St. Thomas, West Indies, the saltness 

 is only -j- 1 7, the enormous amount of fresh water from the Amazon 

 and Orinoco reaching thus far, since a few degrees north of the 

 current the saltness of the ocean is again-]- 2 7. At the Bermuda 

 Islands the saltness is-}- 18.8 the evaporation in the Gulf has been 

 counterbalanced by the waters of the Mississippi. Northward the 

 Gulf Stream increases to 21.0, 22.8, and 23.6 ; but at lat. 43 26', long. 

 44 19' W., where the St. Lawrence empties, the saltness abruptly 

 sinks to -|- 1.5 (a diminution of 2^ thousandths !) From this mini- 

 mum it slowly rises to -f- 18. 9, and at last diminishes again in the 

 higher latitudes. These regular oscillations in tJte saltness of the great 

 Atlantic current show the fresh water supply obtained from the. great 

 African and American rivers, and the effects of evaporation, and 

 make it very probable that these rivers contribute to give the current its 

 particular direction. 



The mean saltness of the polar current of Baffin's Bay is-j- 8. 2, but 

 decreasing towards the north, 



Latitudes, 58 53' 64 69 



Saltness, -f 15.8 -j- 10.3 -j-4 



showing how the water of the Arctic Sea is freshened by the northern 

 rivers, Greenland glaciers, and the Hudson's Bay rivers. 



The saltness of about twenty points of the ocean has been deter- 

 mined for different depths. A difference of about one thousandth 

 corresponds to the greatest depth observed, lat. 12 36' N., long. 25 

 35 r W., depth 11,100 feet. The saltest water of the surface here 

 evidently is the hottest 



In Davis Strait and Baffin's Bay no considerable difference of salt- 

 ness for different depths is observed ; but in the adjacent Atlantic 

 the lower water is less salt than the warmer above it ; and this same 

 cold and less salt bottom current may be traced along the Atlantic, 

 except where great quantities of fresh water are introduced by Euro- 

 pean and American rivers, making the lower strata the saltest. 



In the Indian and Pacific the lowest water everywhere seems to be 

 the saltest (only four observations). 



Composition of the Salts. Twenty-five different elements have 

 been observed in the salt of the ocean or in plants and animals of the 

 sea : 0, H, Cl, Br, I, Fl, 5, P, C, N, Si, Fe, Mn, Mg, Ca, Sr, Ba, Na, 

 Ka : Ag, Cu, Pb, Zn, Co, Ni ; but only those printed in Capitals are 

 predominant. Of these, chlorine, sulphuric acid, lime, and magnesia, 

 may be determined- with great exactitude. Comparing all analyses 

 of ocean water (including the North Sea), it is found that the relative 

 proportion of the components is nearly constant, being 



Chlorine 100, sulphuric acid 11.91, lime 2.95, magnesia 11.08. Total 

 181.1 (for each 100 of chlorine). 



The total is the most constant ; yet there are small but constant 

 differences for the different regions of the ocean differences enlarg- 

 ing with the proximity of land, greatest in gulfs and bays. Silli- 

 man's Journal. 



