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. 



Now in support of such a supposition, it maybe 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. AVhy 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 cau- 

 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 conceive, 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 sec- 

 tion two feet long, with the force which a man could exert ? I 



