348 J. D. Dana on the Origin of Mountains. 
lachian formations. The fact that the folds are Bonar steepest 
on Age northwest side may also be thus acco for. 
x Lne imation of the Appalachians Pee so ay all mountains) 
was Eden tent upon, and the height related to, the thickness of 
nd 
origin; there is no more evidence si local elevation along the 
Apealachieae chain than there is along the plateau in the west. 
io 
vatory movement along the lines of mountain chains.” (¢) er: 
a continental elevation, the nN range eet its present 
shape mainly through erosio 
7. Metamorphism ain first large accumulations of rock 
material; and it went — in the Appalachian region in con- 
aes of the subsiden As to the causes, Professor Hall 
says (p. 77)—after ete to the view of Babba age and Herschel 
increase in thickness of Haldar accumulations—“ Such an increase 
perature would much less than that usually supposed 
necessary for studing metamorphism ; is extremely 
paves if any portion now exposed to observation ever reached 
rature much above that of boiling water. e must, 
chenatiee, look to some other agency than heat* for the es 
~sod th henomena [of metamorphism] witne ; and it 
s that the prime cause must have existed within the material 
itself; and that the entire change is due to motion, or fermenta- 
ion and pressure, aided by, a moderate peep of temperature, 
an chemical change.” 
theory, hive! been shown in my former paper 
* On page 87, Hall observes that the lower beds may be sifleeed ae eh 
that is received from below in consequence of accumulation above; but thi8 
a reason for viel subsiding under accumulating deposits, not 
_ withstanding ‘he Property of heat ordinarily to cause expansion. 
