440 Forbes — Chemistry of the Primeval Earth. 



ordinary volcanic trachyte, and the basaltic rocks from recent 

 volcanoes resemble very closely those from far more ancient periods ; 

 in fact it is often the case that such rocks can only be distinguished 

 from one another by a very careful study of their less prominent 

 characters. 



Taking them as a whole, the main distinction between the erup- 

 tions of the most ancient and most modern epochs is, that in the 

 earliest period the acid rocks, or granites, predominated, whilst at the 

 present day the acid volcanic rocks, or trachytes, are in less propor- 

 tion, the more basic rocks predominating. 



Several reasons to account for this circumstance have been put 

 forward, and are well worthy of consideration. 



To return, however, to Dr. Hunt ; he states that after the 

 energetic action of the acid deluge had ceased, a second similar but 

 slower process of decomposition and solution of the crust commenced 

 by the action of, in this case, carbonic acid with water, resulting ia 

 the formation of clays which remained behind, whilst solutions of 

 the carbonates of soda, lime, and magnesia, poured down into the sea 

 where they precipitated, first the alumina, and subsequently the 

 heavy metals. In such events geologists, although as yet unsuccess- 

 ful in so doing, might still hope to find beds of alumina or of the 

 metallic oxides or carbonates alluded to, amongst the older strata. 

 As no beds of such character are known to occur in nature, this 

 hypothesis must, however, be received with some distrust.^ 



The next assertion of Dr. Hunt, that the limestones have been 

 formed by the precipitation of the lime in the sea by a solution of 

 carbonate of soda, is so decidedly at variance with all the conclusions 

 hitherto arrived at by geologists, zoologists, and microscopists, that 

 it cannot but be disputed, and there is sufficient evidence now 

 produceable to refute this hypothesis. 



In making the assertion, that "the whole of the carbonates of 

 lime which make up the calcareous strata — the marbles and various 

 limestones which we find on the earth's surface are so formed," Dr. 

 Hunt at the same time states that he is quite aware that geologists 

 are of opinion " that these limestones are the result of organic 

 action," but no doubt classes this opinion as another sample of the 

 "fallacious reasoning" which he supposes them to indulge in, and 

 will probably be surprized to learn that zoologists also will dispute 

 his further assertion, that " animals can only appropriate the car- 

 bonate of lime which they find ready formed," and that they, in 

 opposition to this assertion, believe that marine animals can utilise 

 the other salts of lime, existing in abundance in the ocean. 



Had the limestones been so formed by precipitation, whether hot 



1 It may here be remarked that Dr. Hunt, in his lecture, does not allude to what 

 became of the sulphuric acid, which would be the ultimate product of "all the 

 sulphur" burnt into sulphurous acid, and afterwards condensed from the atmosphere 

 into the ocean ; for since it may safely be asserted that there is fully as much (if not 

 more) sulphur as chlorine, the sea formed, according to Br. Hunt's hypothesis, 

 would be as much a solution of sulphate of soda as of seasalt, and he can hardly 

 suppose it to have been precipitated, for it is well known that no beds of sulphate of 

 any importance whatsoever occur in the very oldest formations. 



