PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 478 



Hopkins, that in earlier geological periods the increase of tem- 

 perature in buried strata was far more rapid than at present, so 

 that great heats prevailed at comparatively small depths from the 

 surface and produced great chemical and molecular changes. The 

 temperature at which the various silicated and other minerals, 

 including graphite, were dissolved from the strata and crystalized 

 in the veins, he supposed to have been, judging from various analo- 

 gies, between the melting point of tin and low redness. 



The distinction between the apatite, graphite and magnetite 

 disseminated in the beds and the same minerals in the veins was 

 particularly insisted upon. As to the origin of the principal sili- 

 cious minerals of the limestones, such as serpentine, chondrodite, 

 pyroxene sensellacrite and loganite. Dr. Hunt regards these as 

 having been directly deposited as chemical precipitates from the 

 seas of the time, and cites the example of the Eozoon Canadense, 

 an abundant fossil of the time, found imbedded in these silicates 

 w^hich enclose it, and fill the minute pores of its calcareous skele- 

 ton. To a similar chemical precipitation he attributes the serpen- 

 tines, talcs, chlorites and epidotes which occur in more recent rocks 

 and may be foiind in their incipient state before the metamorpho- 

 sis of these rocks, which has for the most part only crystalized and 

 rearranged the already formed amorphous silicates. The chemical 

 agencies which gave rise to these silicates of lime, magnesia, iron 

 and alumina were briefly discussed, and declared to be still active, 

 although probably to a less degree than formerly. 



The following is a condensed statement of the points discussed 

 by the same author in his paper on 



The Primeval Atmosphere. 

 Dr. Hunt adverted, in commencing, to a theory first put forward 

 by him to explain the chemical conditions of our globe. Starting 

 from the notion of an ingeneous oi-igin, he had contended that the 

 mass probably commenced cooling at the center, and thus gave 

 rise to an anhydrous solid nucleus, having a crust of silicates with 

 an irregular surface, while the chlorine, carbon and sulphur, 

 together with all the hydrogen and an excess of oxygen, formed 

 the atmosphere. As cooling from radiation went on, the first 

 precipitate from this dense atmosphere must have been an intensely 

 acid liquid, which attacking the crust of silicates separated vast 

 amounts of silica and became saturated with earths and alkalies, 

 forming the primeval sea. This condition of things he claimed 



