9S Mr. T. Sterry Hmt 



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 valley, equals the actual vertical thick- 

 ness of the strata comprising them. In the west there has been 

 little or no disturbance, and the highest elevations mark essentially 

 the aggregate thickness of the strata comprising them. In the 

 disturbed regions of the east on the contrary, though we can 

 prove that certain formations of known thickness are included in 

 the mountains, the height of these is never equal to the aggre- 

 gate amount of the formations. " We thus find that in a country 

 not mountainous, the elevations correspond to the thickness of the 

 strata, while in a mountainous country, where the strata are im- 

 mensely thicker, the mountain heights bear no comparative pro- 

 portion to the thickness of the strata." '" While the horizontal 

 strata give their whole elevation to the highest parts of the plain, 

 we find the same beds folded and contorted in the mountain region, 

 and giving to the mountain elevations not one-sixth of their actual 

 measurement." 



Both in the east and west, the valleys exhibit the lower strata 

 of the palaeozoic 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 level, as in 

 the Mississippi valley, the mountains exposed between these 

 valleys, and including the whole palaeozoic series, would have 

 a height of 40,000 feet; so that the mountains evidently 

 correspond to depressions of the surface, which have carried down 

 the bottom rocks below the level at which we meet them in the 

 valleys. In other words, the synclinal structure of these moun- 

 tains depends upon an actual subsidence of the strata along certain 

 lines. 



" We have been taught to believe that mountains are pro- 

 duced by upheaval, folding and plication of the strata, and 

 that from some unexplained cause these lines of elevation exten4 

 along certain directions, gradually dying out on either side, and 

 subsiding at the extremities. We have, however, here shown that 

 the line of the Appalachian chain is the line of the greatest accu- 

 mulation of sediments, and that this great mountain barrier is due 

 to original deposition of materials, and not to any subsequent 

 forces breaking up or disturbing the strata of which it is composed." 



We have given Mr. Hall's reasonings on this subject, for the 

 most part in his own words, and with some detail, for we 



