THE FOSSIL FIELDS OF WYOMING 



The flanks of the range are frequently bedded rocks; in 

 such cases their topography is much more rugged than that of 

 the central portion. 



The variation so noticeable in the topography of the moun- 

 tains, as one range after another is visited, is due to differences 

 in the composition and the hardness of the rocks; differences 

 also in dip often make sharp contrasts in the topography of 

 closely associated areas. 



Some of the ranges visited w^ere w^ell dissected anticlines 

 without a granitic core. The Freezeout Hills is a fine 

 example of this — it is w^ell worthy of the visit of every geologist; 

 nothing in the country is more impressive than this magnificent 

 arch, opened up by subsequent erosion until the whole structure 

 is plainly seen on the lofty cliffs that wall in the subsequent 

 valley. Not only is the extent of the erosion shown but the 

 successive steps of its history are plainly indicated. 



Toward the west the anticline that forms the Freezeouts 

 is barely notched — just a beginning has been made in the great 

 arch of red sandstone — but toward the east the anticline is more 

 and more deeply dissected as one approaches the older portions 

 of the streams that have accomplished the erosion. A pano- 

 rama of age-long activities lies before the observer as he looks 

 along the axis of this great anticline. 



Passing away from the major folds which form the more 

 conspicuous elevations, one meets with numerous lesser folds, 

 which gradually die out as the distance from the mountains 

 increases. These minor folds are generally opened up by 

 erosion, so that the anticlines are well dissected. The hard 

 rocks have not been reduced to the general level of the country, 

 but stand up as rampart-like walls which sweep about as 

 they pass from anticline to syncline, in great curves, forming 



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