Dr. T. Sterry Hunt — On Chemical Geology, 53 



order of their densities. In explanation of this order, he tells us in a note that the 

 zone of carbonic acid gas would be heavier than that of steam, and should, there- 

 fore, come below it. But he forgot that oxygen and nitrogen (or atmospheric air) 

 are also both heavier than steam, and should, consequently, ho. placed below the 

 zone of watery vapor. The specific gravities of carbonic acid and steam are re- 

 spectively 1.525 and 0.624, air being i.ooo. But, apart from this absurd niistake, 

 what shall be said to a man who ignores completely the laws of the diffusion 

 of gases? Will Mr. Forbes kindly explain why, in our present atmosphere, the 

 same elements, namely, oxygen, nitrogen, carbonic acid gas and watery vapour, are 

 commingled, instead of being, as he would have them, arranged in separate zones? 



I have said in my lecture that the first ocean waters would hold in solution salts 

 of alumina and the heavy metals, all of which would be precipitated before the 

 separation of carbonate of lime commenced, in such events, says Mr. Forbes, 

 ''* geologists, though as yet unsuccessful in doing so, might still hope to find beds 0/ 

 alumina or of the metallic oxyds or carbonates alluded tOj in the older strata. As 

 no beds of such character are known to occur in nature^ he regards my view with 

 distrust. Known to Mr. Forbes ! Has he never heard of beds of emery, which 

 are chiefly crystalline alumina, and which occur in the crystalline limestones of 

 Asia Minor, and in the old crystalline schists of New England? Is he ignorant 

 that the beds of bauxite, so abundant in the Mediterranean basin, and used in the 

 manufacture of aluminium, consist chiefly of hydrated alumina ? To console Mr. 

 Forbes, however, I will say that I believe these beds of emery and of bauxite to 

 have been formed by secondary and subsequent reactions, and that we have no- 

 where exposed to view the first-deposited beds, which are everywhere destroyed or 

 buried under more recent strata. When he remembers that the oldest known 

 series of rocks, the Lauren tian, consists of quartzites, limestones, and gneiss, 

 evidently of sedimentary origin, and derived from still older sedimentary rocks, he 

 will understand why he cannot hope to discover the first deposits of alumina or 

 metallic oxyds. These, however, in most cases, have doubtless, by mechanical 

 sub-division, or by solution, been subsequently diffused, and enter into the com- 

 position of later rocks. 



In a note to this paragraph, Mr. Forbes inquires what became of the sulphurous 

 acid of the early atmosphere : as I have already told him, it doubtless became 

 changed into sulphuric acid and passed into the sea. He then says, "it may 

 safely be asserted that there is fully as much (if not more) sulphur than chlorine" 

 in nature, and that according to my hypothesis the sea would become a solution 

 of sulphate of soda. Very safely asserted indeed, since Mr, Forbes takes care to 

 tell us that the sulphur in the form of dense metallic sulphids went to the centre of 

 the earth, which I have shown, I think, good reasons for not believing. As it is, 

 we have only to consider the quantities of sulphids and sulphates in the rocks and 

 waters to see the absurdity of his remarks. 



He next proceeds to discuss the theory of the origin of carbonate of lime. I have 

 said that with the exception that derived from the subaerial decomposition of 

 primitive calcareous silicates, all the carbonate of lime of the earth's surface has 

 been formed from the decomposition of the soluble lime-salts of the sea, by car- 

 bonate of soda (and other soluble carbonates). I, moreover, lay down the propo- 

 sition that "animals can only appropriate the carbonate of lime already formed." 

 In the face of these quotations, cited by Mr. Forbes, he says, as if charging me 

 with holding the view, that if limestones were "formed by precipitation, they 

 would have, from the moment of their deposition, a decided crystalline structure," 

 while " Sorby's microscopical researches prove satisfactorily that all limestones, 

 from the most ancient up to the most recent, ^xe solely foi^med of the debris of organ- 

 isms ;" this will probably be surprising news for Mr. Sorby, and a decisive blow for 

 those who question the organic nature of Eozoon. I am prepared to go as far as any 

 reasonable man in asserting the organic origin of limestones, and have, as every 

 one must see, implied the intervention of organic life, when I say "animals appro- 

 priate the carbonate of lime, etc." The question is, however, whence comes the 

 carbonate of lime to supply the wants of these animals ? Mr. Forbes delares that 

 "zoologists beheve that marine animals can utihze the other salts of lime existing 

 in the ocean," evidently the sulphate or the chlorid of calcium once so abundant 

 there. Will Mr. Forbes or the zoologists explain what has become of the acids 

 once combined with the lime which has built up the thousands of feet of limestone 



