iS95. RESULTS OF ^'CHALLENGER" EXPEDITION. 17 



In the Atlantic and Pacific Oceans the controHing influence of 

 the great anticyclones of the lower latitudes is very clearly seen even 

 at great depths. Circulation is, of course, most active in the 

 Atlantic, partly because the belt of calms between the trades is at all 

 seasons north of the equator, and the trades themselves blow with 

 greater force and persistency than in the Pacific, and partly because 

 the configuration of the land is such that the horizontal movements of 

 water at and near the surface are suddenly arrested, and the increased 

 pressure due to the heaping up of the waters is in part relieved by 

 vertical movements downwards. One important effect of the position 

 of the belt of calms is that immense quantities of warm surface 

 water are transferred bodily from the South to the North Atlantic, 

 with the result that so far as temperature is concerned the two oceans 

 stand in strong contrast to each other even at great depths. A com- 

 parative study of the distribution of temperature in the Atlantic and 

 Pacific Oceans strongly impresses upon us the truth of Mr. Buchanan's 

 remark, recently emphasised by Admiral Wharton, as to the extreme 

 slowness of the vertical movements of oceanic waters when the action 

 of gravity is left to work alone. If we take a sea-water of average 

 density, 1*0260 at 60° Fahr., its density at 45° Fahr. is 1-0275, and 

 at 67° Fahr. 1*0250; so that the same water can cover the whole 

 range of density found in the Atlantic by a temperature variation 

 of 22° Fahr. Hence, even the saltest surface-waters can only pene- 

 trate the layers underlying them after having been cooled by a 

 process of mixture, which has probably robbed them by dilution of 

 the greater part of the extra salinity ; and we are forced to the 

 conclusion that when strongly-marked vertical movement occurs it 

 must, in most cases, be ascribed to differences of pressure acting 

 at the surface. 



In the latter part of his discussion Dr. Buchan treats the Gulf 

 of Mexico, the Mediterranean, the Red Sea, the Persian Gulf, the 

 Indian Ocean, the Arctic Ocean and Norwegian Sea, and the 

 Southern Ocean under separate headings. Outside the Atlantic and 

 Pacific, interest naturally centres in the last-named, with which is 

 inseparably bound up the Indian Ocean. The rigours of the unknown 

 Antarctic are kept within bounds by the vast quantities of heat sent 

 southward from the Brave West Winds and their following currents. 

 At the surface the icy fingers are only visible here and there across 

 the surface of the warm drifts, but underneath, 1,500 fathoms down, 

 the creeping cold can be seen making its way northwards. 



H. N. Dickson. 



III.— GEOLOGY. 



Geologists received from the "Challenger" a great mass of facts 

 concerning the deposits now forming in the depths of the ocean ; 

 their interest was again markedly aroused in the problems of coral- 

 reefs and the solution of limestone ; while for the discussion of those 



c 



