194 Igneous Rocks and Volcanos. 



AET. XXI. — On the Theory of Igneous Rochs and Volcanos. By 

 T. Sterry Hunt, of the Geological Survey of Canada. 



(Read before the Canadian Institute, 13th March, 1858.) 



In a note in the American Journal of Science for January, 

 1858, I have ventured to put forward some speculations upon the 

 chemistry of a cooling globe, such as the igneous theory supposes 

 our earth to have been at an early period. Considering only the 

 crust with which geology makes us acquainted, and the liquid 

 and gaseous elements which now surround it, I have endeavored 

 to show that we may attain to some idea of the chemical con- 

 ditions of the cooling mass by conceiving these materials to again 

 re-act upon each other under the influence of an intense heat. 

 The quartz, which is present in such a great proportion in many 

 rocks, would decompose the carbonates and sulphates, and aided 

 by the presence of water, the chlorids both of the rocky strata 

 and the sea, while the organic matters and the fossil carbon 

 would be burned by the atmospheric oxygen. From these reac- 

 tions would result a fused mass of silicates of alumina, alkalies,- 

 lime, magnesia, iron, etc., while all the carbon, sulphur and chlo- 

 rine, in the form of acid gases,. mixed with watery vapour, azote, 

 and a probable excess of oxygen, would form an exceedingly 

 dense atmosphere. When the cooling permitted condensation, an 

 acid rain would fall upon the heated crust of the earth, decompos- 

 ing the silicates, and giving rise to chlorids and sulphates of the 

 various bases, while the separated silica would probably take the 

 form of crystalline quartz. 



In the next stage, the portions of the primitive crust not covered 

 by the ocean, undergo a decomposition under the influence of the 

 hot moist atmosphere charged with carbonic acid, and the felds- 

 pathic silicates are converted into clays with separation of an 

 alkaline silicate, which, decomposed by the carbonic acid, finds 

 its way to the sea in the form of alkaline bicarbonate, where, 

 having first precipitated any dissolved sesquioxyds, it changes the 

 dissolved lime-salts into bicarbonate, which precipitated chemi- 

 cally or separated by organic agencies, gives rise to limestones, 

 the chlorid of calcium being at the same time replaced by com- 

 mon salt. The separation from the water of the ocean, of gypsum 

 and sea-salt, and of the salts of potash, by the agency of marine 

 plants, and by the formation of glauconite, are considerations 

 foreign to our present study. 



