UINTA STRUCTURE. 11 



fine illustration of this type of structure. The mountain is divided into two 

 unequal parts by a canon, through which the Yampa River runs. The 

 axis of the mountain has a north and south direction. 



Figure 1 is a section through this mountain, in a north and south direc- 

 tion, along the axis of upheaval. Figure 2 is a section through it in a 



transverse direction. 



i 



CONCOMITANT FORMS. 



1. Monoclinal Ridfjes on the Flanks. Under conditions which are so well 

 known as to need no further explanation here, monoclinal ridges or hog- 

 backs are formed on the flanks of such upheavals, and sometimes such 

 monoclinal ridges are of such magnitude as to be dignified with the name of 

 mountains. Where two or more series of indurated, inclined beds are sep- 

 arated by extensive series of softer material, two or more monoclinal ridges 

 may be formed. 



2. Monoclinal Ridges only. Sometimes we find that an anticlinal up- 

 heaval has been eroded in intaglio, so that there is no great central moun- 

 tain mass, but the axis of upheaval is the site of a valley or low plain, but 

 the monoclinal ridges on the flanks remain. 



3. Inclined Plateaus. Where the anticlinal upheaval has a great ampli- 

 tude, as compared with the vertical uplift, the beds incline but slightly. 

 Under such conditions inclined plateaus or mesas are found instead of 

 monoclinal ridges, usually having steep escarpments facing the axis of the 

 flexure. 



III. UINTA STRUCTURE. 



In the Uinta Mountains we have a great range carved from an anticlinal 

 upheaval, the axis of which has an easterly and westerly trend, and is more 

 than one hundred and fifty miles in length. It terminates abruptly against 

 the Wasatch Mountains on the west and is cut off by the short, abrupt anti- 

 clinal of Junction Mountain on the east, the latter having its axis in a north 

 and sQuth direction. There are several important facts observed in the 

 study of this great flexure. Its axis has been lifted above the level of the 

 sea about thirty thousand feet, and above the level of the adjacent country 



