244 STRUCTURAL GEOLOGY. 



Thickness of Mountain Sediments. We have said 

 that mountains are composed of enormously thick sedi- 

 ments, crushed together horizontally with many crump- 

 lings, and swelled up proportionally. We will now give 

 examples of such thickness. The Appalachian consists 

 of folded strata (Fig. 147) which, according to Hall, are 

 not less than 40,000 feet, or nearly eight miles, in thick- 

 ness. The Wahsatch consists of sediments which, ac- 

 cording to King, are 50,000 feet, or nearly ten miles, in 

 thickness. The Coast Eange of California consists of 

 folded cretaceous and tertiary. The cretaceous alone, 

 according to Whitney, are 20,000 feet thick. The tertiary 

 have not been measured, but cannot be less than 10,000 

 feet. So that at least 30,000 feet, or nearly six miles, 

 thickness of sediments are involved in the folded struc- 

 ture of this range (Fig. 146). The strata of the Alps are 

 not less than 40,000 to 50,000 feet thick. The same is 

 true of all mountains. 



Now, we must not imagine that this is evidence of the 

 average thickness of strata, but only revealed in moun- 

 tains by erosion, for the very same strata elsewhere are 

 much thinner. For example, the same strata, which are 

 40,000 feet thick in the Appalachian Eange, thin out west- 

 ward until they are only 4,000 feet thick at the Mississippi 

 River. The very same strata, which are 30,000 feet thick, 

 in the Wahsatch, thin out eastward, and are only 1,000 

 feet thick on the Plains. Thus, then, mountain-ranges, 

 before they ivere upheaved,, were lines of exceptionally thick 

 sediments. This may be regarded as certain. 



Mountain-Ranges are Upheaved Marginal Sea- 

 Bottoms. Where, then, do we find exceptionally thick 

 sediments ? Where, but along marginal sea-bottoms ? 

 We have seen (page 48) that here are accumulated nearly 

 the whole debris of continental erosion. Therefore, 

 mountain-ranges before they luere upheaved, were mar- 

 ginal sea-bottoms on which have accumulated enormously 



