76 J. G. Goodchild — The Paste of Limestones. 



The one explanation that would have satisfied all the requirements 

 of the field geologist is, that the greater part, or the whole, of the 

 paste in question is mainly due to chemical precipitation. But 

 until quite lately chemists assured .us that the facts then known 

 did not warrant the assumption that any precipitation whatever of 

 carbonate of lime was possible in the open sea. This view was 

 mainly based upon the fact that all analyses of sea- water showed 

 that the percentage of carbonate of lime held in solution was but 

 a small fraction (a tenth, or thereabouts) of what sea-water was 

 capable of dissolving. Therefore, it was pointed out, precipitation 

 of carbonate of lime was simply impossible. That is no doubt 

 perfectly true so far as it goes. But were the reactions that had been 

 considered the only ones possible ? More recent researches have 

 shown that they are not. • To these I shall refer in more detail 

 presently. In this connection one very curious fact must surely 

 have struck others engaged in teaching geology, as it struck me. 

 In dealing with the enormous quantities of cai'bonate of lime that 

 the rivers of the world are carrying seawards, one is called upon to 

 explain how it happens that, off the mouths of those rivers, an 

 analysis of the sea-water fails to show more than a trace of either 

 carbonic acid or carbonate of lime. On the contrary, the composition 

 of the sea-water there is practically identical with that of the ocean 

 far from land. What has become of the carbonate of lime? We 

 are told that it has been assimilated by organisms. That seems 

 a reasonable explanation at first sight. But where are the organisms 

 that effect this remarkable change so rapidly ? Surely no one is 

 prepared to maintain that the animals and the plants that build up 

 organic cai'bonate of lime come to the mouths of rivers specially to 

 obtain the supplies necessary for their purpose ? The facts tell 

 quite the other way. Indeed, the proportion of such organisms 

 living just where river-water and sea-water mingle, to those living 

 out at sea, is almost infinitely small. In other words, where 

 carbonate of lime in solution is in excess, the percentage of organisms 

 with calcareous frameworks is probably not as high as it is where 

 the carbonate of lime is known to be deficient. If for that reason 

 alone, it is quite clear that such an explanation is at fault. 



If the carbonate of lime has not been extracted by organic 

 agencies, then it must have disappeared through some reaction 

 between the solutions of carbonate of lime in carbonated fresh water 

 on the one hand and the saline constituents of sea water on the 

 other. In other words, the carbonate of lime has passed into some 

 other compound. What the exact nature of that compound is must 

 be left to chemists to decide. But it is stated by Dr. Sterry Hunt, 

 that if a solution of carbonate of lime in carbonated water be mixed 

 with a solution of sulphate of magnesia in water, double decom- 

 position ensues, and carbonate of magnesia and sulphate of lime 

 are formed. Magnesian sulphate exists in sea-water in proportions, 

 per 1000 parts of water by weight, varying from 2-20 to 640. If this 

 is really in accordance with the results of modern researches, then 

 we seem here to obtain ' a clue as to what is happening. The 



