254 



STRUCTURE COMMON TO ALL ROCKS. 



and which, occur in nearly all mountains, can not be produced except by 

 lateral pressure, and are therefore proof of such pressure. But, more- 



Fig. 226.— Section of a portion of the Alps. 



over, it can be shown that, when we take into consideration the im- 

 mense thickness of mountain strata and the degree of folding, lateral 

 pressure is sufficient to account for the whole elevation, without calling 

 in the aid of any upward pushing from beneath. For example, the 

 Coast Eange of California (Fig. 224) is composed of at least five anti- 

 clines and corresponding synclines.* If its folded strata were spread out 

 horizontally in the position of the original sediments, they would un- 

 doubtedly cover double the space. Now, supposing the strata here are 

 only 10,000 feet thick — a very moderate estimate — in mashing to one 

 half the extent, they would be thickened to 20,000 feet, which would 

 be a clear elevation of 10,000 feet if they had not been subsequently 

 eroded. According to Eenevier,f a section of the Alps reveals seven 

 anticlines and corresponding synclines, and some of these are complete 

 over-folds (Fig. 226). AYe are safe in saying that Alpine strata have 

 been mashed horizontally into one third their original extent. Sup- 

 posing these were originally 30,000 feet thick (they were really much 

 thicker), this would make a clear elevation of 60,000 feet. Of course, 

 most of this has been cut away by erosion. In the Appalachian range, 

 according to Claypole,J; the foldings are so extreme that in one place 

 95 miles of original extent have been mashed into 16 miles, or six into 

 one, and yet the Appalachian strata are estimated as 40,000 feet thick. 

 Oases of still greater doubling of strata upon themselves occur. In the 

 Highlands of Scotland the strata by lateral thrust first rose in a fold, 

 then were pushed forward into an over-fold, then broken and slidden 

 one over another for ten miles.* In the Canadian Rocky Mountains 

 there is an overthrust of seven miles, by which the Cambrian is made 



* American Journal of Science, vol. ii, p. 297, 1876. 

 f Archives des Sciences, vol. lix, p. 5, 1877. 



± American Naturalist, vol. xix, p. 257, 1885. 



* Geike, Nature, vol. xxix, p. 31, 1884. 



