390 THE POPULAR SCIENCE MONTHLY. 



turn around this great obstruction, rather than pass through it ? The 

 answer is, that the river had the right of way ; in other words, it was 

 running ore the mountains were formed : not before the rocks, of which 

 the mountains are composed, were deposited, but before the formations 

 were folded, so as to make a mountain-range. 



The contractine: or sliriveling of the earth causes the rocks near 

 the surface to wrinkle or fold, and such a fold was started athwart the 

 course of the river. Had it been suddenly formed, it would have been 

 an obstruction sufficient to turn the water in a new course to the east, 

 beyond the extension of the wrinkle ; but the emergence of the fold 

 above the general surface of the country was little or no faster than 

 the progress of the corrasion of the channeh We may say, then, tliat 

 the river did not cut its way down through the mountains, from a 

 height of many thousand feet above its present site ; but, having an 

 elevation differing but little, perhaps, from what it now has, as the 

 fold was lifted, it cleared away the obstruction by cutting a canon 

 and the walls were thus elevated on either side. The river j^reserved 

 its level, but mountains were lifted up ; as the saw revolves on a tixed 

 pivot, while the log through which it cuts is moved along. The river 

 was the saw which cut the mountains in two. 



Recurring to the time before this wrinkle was formed, there "were 

 beds of sandstone, shale, and limestone, more than 24,000 feet in thick- 

 ness, spread horizontally over a broad stretch of this country. Then 

 the summit of the fold slowly emerged, until the lower beds of sand- 

 stone were lifted to the altitude at first occupied by the upper beds, 

 and if these upper beds had not been carried away, they would now 

 be found more than 24,000 feet above the river, and we should have a 

 billow of sandstone, with its axis lying in an easterly and westerly 

 direction, more than 100 miles in length, 50 miles in breadth, and over 

 24,000 feet higher than the present altitude of the river, gently 

 rounded from its central line above to the foot of the slope on either 

 side. But as the rocks were lifted, rains fell upon them and gathered 

 into streams, and the wash of the rains and the corrasion of the rivers 

 cut the billow down almost as fast as it rose, so that the present alti- 

 tude of these mountains marks only the difference between the ele- 

 vation and the denudation. 



It has been said that the elevation of the wrinkle was 24,000 feet, 

 but it is probable that this is not the entire amount, for the present 

 altitude of the river, above the sea, is nearly 6,000 feet, and when this 

 folding began we have reason to believe that the general surface of 

 this country was but slightly above that general standard of com- 

 parison. 



Then there were down-turned as Avell as up-turned wrinkles, or, as 

 the geologist would say, there were synclinal as well as anticlinal 

 folds. Had there been no degradation of the fold, there would have 

 been a bed of i*ock turned over its summit 24,000 feet above the pres- 



