256 Mr. John Murray [March 16, 



must be in a continual state of flux as to its internal composition. 

 While the quantity of sea salts in a given volume of water varies 

 with position, yet it has been shown by hundreds of analyses that the 

 actual ratio of acids and bases — that is, the ratio of the constituents of 

 sea salts — is constant in waters from all regions and depths, with one 

 very significant excei)tion — that of lime — which is present in slightly 

 greater proportion in deep water. 



The total amount of calcium in a cubic mile of sea water is esti- 

 mated at nearly 2,000,000 tons. The amount of the same element 

 present in a cubic mile of river water is nearly 150,000 tons. 

 At the rate at which rivers carry down water from the land it is 

 estimated that it would take 680,000 years to pour into the ocean 

 an amount of calcium equal to that now held by the ocean in 

 solution. 



The amount of calcium existing in the 40,000,000 square miles 

 of the typical calcareous deposits of the ocean exceeds, however, that 

 at present held in solution if we merely t^ke them to have an average 

 thickness of 30 feet, and from this calculation we might say that, if 

 the secretion and solution of lime in the other regions of the ocean 

 be exactly balanced, and the calcium in the ocean remain always 

 constant, those calcareous deposits of the thickness indicated would 

 require between 600,000 and 700,000 years to accumulate. There is 

 good evidence, however, that the rate of accumulation is much more 

 raj^id in some positions. 



The lime thus carried down to the sea is originally derived from 

 the decomposition of anhydrous minerals, and comes from the land in 

 the form of carbonate, phosphate, and suljDhate of lime — the carbonate 

 being in the greatest abundance in river water. On the other hand, 

 the sulphate of lime very greatly predominates in sea water, the 

 carbonates being present in small quantity. We are not in a position 

 to say whether or not the coral polyps take the whole of the material 

 for their skeletons from the carbonates, as is generally believed, or 

 indeed to say what changes take place during the progress of secretion 

 by organisms. 



In the greatest depths of the Pacific coral seas there is striking 

 evidence of the solvent power of ocean water. Our dredges bring up 

 from a depth of three or four miles over a hundred ear-bones of 

 whales and remnants of the dense Ziphioid beaks, but all the larger 

 and more areolar bones of these immense animals have been almost en- 

 tirely removed by solution. In a single haul there may also be many 

 hundreds of sharks' teeth, some of them larger than the fossil Carcha- 

 rodon teeth, but all that remains of them is the hard dentine. None 

 of the numerous calcareous surface shells reach the bottom, although 

 they are quite as abundant over the red clay areas as over those 

 shallower areas where they form Globigerina and Pteropod dej)osits. 

 In consequence of the small amount of detrital material reaching 

 these abysmal areas distant from continents, cosmic metallic spherules, 

 manganese nodules, highly altered volcanic fragments, and zeolitic 



