INTRODUCTION. TT 



temperature has permeated the entire mass. Still such an increase of 

 temperature would be much less than that usually supposed necessary 

 for producing metamorphism ; and it is extremely doubtful if any por- 

 tion now exposed to observation ever reached a temperature much 

 above that of boiling water*. We must therefore look to some other 

 agency than heat for the production of the phenomena witnessed; and 

 it seems that the prime cause must have existed within the material 

 itself, and that the entire change is due to motion, or fermentation and 

 pressure, aided by a moderate increase of temperature producing che- 

 mical change. The chemical investigations in the Canada Geological 

 Survey, carried on by Mr. T. Stebry Hunt, have shown that the un- 

 metamorphosed rocks of the lower part of the Appalachian chain, 

 or those of the age of the Hudson-river group, contain the same mine- 

 ral substances and in precisely the same proportions as the metamor- 

 phosed crystalline and subcrystalline beds of the adjacent region, where 

 the segregated minerals become palpable and visiblef. Moreover, in 

 the same survey the identity of the metamorphic and non-metamorphic 

 rocks had been determined by actual continuity of the beds. 



Without intending to discuss the chemical question, it seems to me 

 that the first requisite of metamorphism is the aggregation or accumu- 

 lation of sedimentary matter and chemical precipitates in large quanti- 

 ties and in great thickness upon the sea bottom. Over the entire area, 

 where these older deposits are thin, there is no evidence of pervading 



• Whatever this temperature itiay have been, it was doubtless the same, and no other, that would 

 be reached by penetrating to an equal depth beneath the crust ; and in the process of depression of 

 theee gedimentary strata, they have unquestionably reached a comparatively high degree of tempera- 

 ture. Or to speak in accordance with the ordinarily accepted view, the accumulation of the sedimenta 

 has disturbed the equilibrium of temperature, causing a rise, or movement towards the surface, of the 

 isothermal lines or strata, corresponding to the amount or thickness of the accumulation. But if we 

 look a little farther at this matter, and admitting that there is a maximum thickness of forty thou- 

 sand feet, we cannot suppose that the metamorphosed portions now exposed have ever reached this 

 depth below the surface, or a temperature corresponding to such depth below the surface. On the 

 other hand, I do not suppose that those parts now visible have reached a temperature, or have been 

 depressed to the extent, of an equivalent of twenty thousand feet. 



t The investigations of Mr. Hunt, in this direction, are bringing out results of the highest interest, 

 and such as will, I believe, when combined, achieve a complete revolution iu this department of 

 geological science. 



