202 Dr. Hunt on the Chemistry of the Earth, 



porters, and which supposes that the magnesia was introduced 

 subsequent to the deposition of the sediments, by a " certain mys- 

 terious action of intrusive pyroxenic rocks," which have been ejected 

 in the vicinity of deposits of pure limestone. Mr. Cordier also 

 combats the idea that these last have been formed entirely of the 

 debris of testacea and zoophytes, which according to him, form 

 but a small proportion of limestone formations. Going back still 

 farther, he finds the source alike of the carbonate of lime of these 

 organic remains, and of the great mass of calcareous rocks, in cer- ' 

 tain chemical reactions. The pure limestones, according to him, 

 pass into magnesian limestones by an admixture of dolomite, and 

 form thus a transition to the pure dolomites, so that we must ad- 

 mit a common origin for all these rocks. The source of the two 

 carbonates which compose them, according to Mr. Gordier, is to 

 be found in the reaction of carbonate of soda upon the chlorids of 

 calcium and magnesium in sea-water ; the carbonate of soda 

 being derived from the decomposition of feldspars, from alka- 

 line springs, and from plutonic emanations. This alkaline salt, 

 reacting upon the salts of sea-water, would give rise to chlorid of 

 sodium and carbonate of lime, and under certain conditions, to 

 calcareo-magnesian precipitates. From this reaction must result 

 a secular variation in the composition of the ocean, which cor- 

 responds to the progressive changes in the marine fauna of suc- 

 cessive geological epochs. 



Such is the theory of Mr. Cordier, which is now published, for 

 the first time, in 1862 ; and which I have thus noticed in order to 

 call the attention of the Academy to my own published papers, in 

 which I have maintained similar views for the last four years. In 

 The American Journal of Science for January, 1858, 1 endeavored, 

 in admitting the igneous theory of the earth's origin, to obtain some 

 notion of the chemical conditions of the cooling globe,by supposing 

 the matters which now form the earth's crust to be fused together 

 by an intense heat. From this would result an atmosphere hold- 

 ing, in the state of acid gases, all the carbon, the sulphur, and the 

 chlorine, besides the elements of air and water ; while the bases, 

 such as the alkalies, lime, magnesia, oxyd of iron and alumina, in 

 combination with silica, would form the solid crust. This would 

 afterwards be attacked by the acids precipitated, with water, un- 

 der the pressure of a high atmospheric column, and at an elevated 

 temperature ; from which would result the separation of a great 

 amount of silica, and the formation of an ocean, whose waters 



