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THE POPULAR SCIE^^CE MONTHLY. 



relation to the surface of t])e sea, so that upheaval or throw is only 

 relative to this general standard of comparison. But during the geo- 

 logical ages represented in the folding and carving of the Uinta Moun- 

 tains, it is possible the level of the sea itself has been changed by the 

 shrinking of the earth, and a part, at least, of the apparent upheaval 

 above mentioned may be accounted for by a depression of the forma- 

 tions in synclhial folds, and the letting down of broad areas of the 

 earth's surface by lateral contraction exhibited, in corrugation. 



Fig. 5. An Anticlinal Valley, with Section. 



It has already been said that the cutting off of the fold has left the 

 upturned edges of the formations exposed to view. Some of these 

 beds are quite hard, others are composed of very soft material; so 

 that there are alternating beds of harder and softer rocks running in 

 an easterly and westerly direction, both on the north and south side 

 of the range. The soft rocks, yielding much more readily to atmos- 

 pheric degradation, have been washed out in irregular valleys, be- 

 tween intervening ridges of harder rock, so tliat we have a series of 

 nearly parallel valleys, and also a series of intervening parallel ridges, 

 and both valleys and ridges are approximately parallel to the range. 

 But, as the great fold of the Uinta Mountains is greatly com])licated 



