PHILOSOPHICAL SOCIETY OF WASHINGTON. 49 



of the sea. On the east, the rim of the basin of the Colorado 

 is set with snow-clad mountains, rising from eight to nearly fifteen 

 thousand feet above the level of the sea ; and on the west, bj 

 mountains and plateaus rising from eight to twelve thousand feet. 

 The grand anticlinal folds cross this portion of the valley from 

 east to west. The most northern of these is marked by the east- 

 ern Uintah Mountains. This range, well defined on the west, 

 extends to the east across Green River until it becomes involved 

 with the profound transverse poles of the Rocky Mountains. 

 The up-turned axis of the second pole crosses the Yalley of the 

 Colorado about twenty miles south of the junction of the Grand 

 and Green, and is lost in the Wasatch piateau in the west. Its 

 eastern extension has been examined to a distance of about thirty 

 miles from the river. The up-turned axis of the third fold crosses 

 the valley along a line a little south of the Colorado-Chiquito. 

 If the first fold had been lifted up without denudation pari passu, 

 its summit would be about 27,000 feet above what is now the bed 

 of the river, or about 32,500 feet above the level of the sea. 

 Under the same supposed conditions, the summit of the second 

 fold would be about 22,000 feet above the level of the sea; and 

 the third fold about 32,500 feet. 



This region is also traversed by folds, the axes of which are in 

 lines running in a north and south direction. These folds have 

 displaced the strata from 50 to 1500 feet; are variable in length, 

 the shortest observed being about 12 miles, the longest about 110, 

 and are scattered irregularly over the country. 



Mr. Powell then discovered and discussed the system of 

 drainage that would have obtained had these folds been lifted up 

 simultaneously and without denudation, until the displacement 

 of the formations was completed. 



He then explained the system of drainage actually found. This 

 led to a classification of the valleys or lines of drainage. 



Yalleys have been observed to occur running in a direction 

 along the synclinal axis of folds; others along the anticlinal axes. 

 Other valleys were observed running in a direction with the folds, 

 but located between the up-turned and down-turned axes. The 

 slope on the side next to the anticlinal axis conforming in a gen- 

 eral way with the dip of the formations. The slope on the side 

 next to the synclinal axis was usually found more abrupt, and 

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