270 Address before the Association of American Geologists. 
ridges ; and if more powerful along the western than the eastern 
side, they might fall over so as to take an inverted dip, without 
producing any remarkable dislocations, while subsequent denuda- 
tion would give to the surface its present outline. e 
Now in support of such a supposition, it may be said, first, that 
it would satisfactorily explain the present position of the strata. , 
For if they could now be lifted up and made to dip in an opposite 
direction, every thing, for the most part, would be brought right ; 
that is, the natural order of superposition would be restored. -Se* 
condly, this supposition explains the moderate dip of the rocks in 
the valleys, and the gentle slope of the mountains on their east- 
ern sides, and the abrupt escarpment of their western sides. 
Thirdly, the occurrence of thermal springs along many of these 
folded axes, as is the case in New England and Virginia, and the 
extensive dolomitization of the limestone in the valleys, afford 
presumptive evidence of long lines of fracture, just where, by this 
hypothesis, they ought to exist. Fourthly, we should readily ad- 
mit that such a plication and inversion of the strata might take 
place on a small scale. If for instance, we were to press against 
the extremities of a series of plastic layers two feet long, they 
could easily be made to assume the position into which the rocks 
under consideration are thrown. Why then should we not be 
equally ready to admit that this might as easily be done, over a 
breadth of fifty miles, and a length of twelve hundred, provided 
we can find in nature, forces sufficiently powerful ?. Finally, such 
forces do exist in nature, and have often been in operation. After 
we have admitted, as every geologist does admit, that the exist- 
ing continents and mountains: of the globe have been elevated 
from the ocean’s bed, there is scarcely any effect, short of an im- 
possibility, which we may not impute to the same agency. Merely 
for illustration, without maintaining its truth, let us suppose with 
Beaumont, that the vertical movements of our continents result 
from the shrinking of the internal parts of the earth, which cal 
ses a plication of its crust, simply by the force of gravity. And 
Suppose the present crest of the Appalachian and Green moun- 
tains to have formed the line of least resistance on this continent 
Is it difficult to conceivé, that by such a power, a broad belt of 
the earth’s crust, more than a thousand miles long, might have 
been ridged and overturned, with just as much facility, as a S€¢- 
tion two feet long, with the force which a man could exert? ! 
