V.] THE ORIGIN OF MOUNTAINS. 51 



never equal to the aggregate 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 immensely thicker, the mountain 

 heights bear no comparative proportion to the thickness of the 

 strata While the horizontal strata give their whole ele- 

 vation to the highest parts of the plain, we find the same beds 

 folded and contorted in the mountain region, and giving to the 

 rnountian 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 be- 

 tween 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 struc- 

 ture of these mountains depends upon an actual subsidence of 

 the strata alon^ 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 ex- 

 tend 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 accumulation 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 

 conceive that the views which he is here urging are of the 

 highest importance to a correct understanding of the theory of 

 mountains. In the Canadian Naturalist for December, 1859, 

 p. 425, and in the American Journal of Science (2), XXX. 137, 



