INTRODUCTION. 
77 
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. Sterry 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 may 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 
these sedimentary 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 sediments 
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. 
f 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 in this department of 
geological science. 
