Forbes — Chemistry of the Primeval Earth. 437 



posed of substances all of the same degree of fusibility, neither of 

 which views are likely to meet with general acceptation. 



The density of the exterior of the earth with which geologists are 

 acquainted, is known to be only about one-half of the mean density 

 of the earth's mass as a whole, and at first this was accounted for 

 upon the supposition that its components became more and more 

 dense in depth, owing to the pressure of the superiacumbent mass ; 

 experimental research tends, however, to show that a limit is soon 

 reached, beyond which the compression or increase of density 

 becomes less and less in relation to the force employed ;^ and there 

 are consequently strong reasons for believing that the central parts of 

 the globe must consist of much denser bodies, such as metals and 

 their metallic compounds. 



As we well know that such metallic bodies are iafinitely more 

 easily fusible than the silicious rocks of the superficial crust, it may 

 be fairly advanced, that the difference between the fusing points of 

 these bodies would more than counterbalance the iafluence of pres- 

 sure in causiug solidification at the centre of the globe, by the 

 elevation of the temperature at which the central mass could remain 

 in fusion.^ 



The above reasons make the author come to the conclusion that 

 Dr. Hunt has not produced sufiicient evidence to prove that the 

 earth is really entirely solid; and he still adheres to the opinion 

 that the earth does enclose a vast reservoir or reservoirs of still fluid 

 igneous matter in its interior. 



The chemical composition of the cooling globe, and specially of 

 its external crust, next demands consideration. Dr. Hunt believes 

 the primitive crust to have been composed of the alkalies, alkaline 

 earths, earths and metallic bases in combination with silica, and 

 surrounded by a dense acid atmosphere, consisting of hydrochloric, 

 sulphurous, and carbonic acids, along with steam, nitrogen, and 

 probably the excess of oxygen. The author would protest against 

 such an atmosphere, and for reasons about to be explained, does not 

 believe that it ever did or could have existed. 



We are told in the first place, that " all the sulphur would be 

 diffused in the atmosphere as sulphurous acid." The author, on the 

 contrary, believes that the sulphur would have combined with the 

 heavy metals, forming dense sulphides, which would at once sink 

 below the lighter external crust and there be protected from oxida- 

 tion. Nor does he consider it probable that at such a moment of 

 general combiuation an "excess of oxygen" could possibly be 

 present in an atmosphere highly charged with sulphurous acid. 



Dr. Hunt alleges that we should find " all chlorine in the form 

 of hydrochloric acid," which is also contrary to the opinion of the 



1 And the author thinks it probable that the same would also be the case with the 

 relations of fusing points to pressure. 



2 In opposition to this view, it might be said that the densest of all metals, Plati- 

 num, is also one of the most infusible. To this we answer, that many of the 

 compounds of Platinum, say with zinc, tin, arsenic, etc., are so extremely fusible as to 

 melt in the flame of a candle. 



