American Geology, by T. 8. Hunt. 407 
the Mississippi pared’ heaped the carboniferous ae 
which is wanting i east, have, according to all, a 
thickness of scarce 2000 “feet. In many places in chit valley 
we find the Silurian formations exposed, exhibiting hills of 1000 
feet, made of horizontal strata, with the Potsdam sandstone for 
their base, and capped by the Niagara limestone, while the same 
strata in the Appalachians would give them ten to sixteen times 
that thickness. Still, as Mr. Hall remarks, we have there no 
mountains of corresponding altitude, that is to say, none whose 
height, like those of the Mississippi ee equals the actual 
vertical thickness of the strata com pri them. In the west 
there has been little or no distasbanod fai the highest eleva- 
tions mark essentially the aggregate thickness of the strata com- 
prising them. In the distarbed regions of the east on the con- 
trary, though we can prove that certain formations of known 
thickness are inc luded in the mountains, m9 height of these is 
never equal to the aggregate amount of t e formations. “ 
thus find that in a country not antibistsen the elevations cor- 
respond to. the thickness ‘of the strata, while in a mountainous 
country, where the strata are immensely thicker, the mountain 
heights bear no comparative proportion to the thickness of the 
strata.” “ While the horizontal reese give their whole elevation 
to the highest parts of the plain, e same beds folded 
and contorted in the mountain region and giving a no jmoun- 
tain elevations not one-sixth of their actual caavite 
oth in the east and west, the vallefe exhibit the caees strata 
of the palseozoic series, and it is evident that had the eastern 
region been elevated without folding of the strata, so as to make 
the base of the series correspond nearly with the sea wee as in 
the Mississippi valley, the mountains exposed between these 
valleys, and including the whole paleozoic series, outed have 
a height of 40,000 feet: so that the mountains evidently corres- 
pond to depressions of the surface, which have carried down the 
ottom rocks below the level at which we meet them in the val- 
leys. In other words the synclinal structure of these mountains 
wee an actual subsidence of the strata along certain 
i 
We have been taught to believe that mountains are produced 
by opheaval, folding and plication of the strata, and that from 
some unexplained cause these lines of elevation extend along 
* In Michigan according to the late report of Prof. When ne “yee observed 
thickness of the strata from the top of the Sault St. top of 
the carboniferous series is little over 1790 feet, divic are! as rr bens Peenton and 
Hudson River groups, 50 feet, Upper Silurian 185, Devonian 782, Carbonifvrous 
ur 
cann 
und 169 feet of gypsiferous marls, which yield strong brine springs, 
Am. Jour. Scr.—Seconp Serts, Vou. XXXI, No, 93.—May, 1861. 
53 
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