442 F. B. WEEKS STRATIGRAPHY OF THE UNITA RANGE 



where the shales have been faulted and the relations of the formations 

 can not readily be determined. 



On the northern flank of the eastern Uinta several bands of conglom- 

 erate are interbedded with the "Uinta" sandstones, and have considerable 

 areal extent. They are well exposed in cliffs, have the same strike and 

 dip, and form an integral part of the "Uinta" series. 



Berkey noted (8) an imconformity by erosion within the Carboniferous, 

 and suggested that by a withdrawal of the sea slowly westward and a 

 more rapid readvance to its former boundaries the erosion interval in the 

 Green Eiver region noted by Powell should be extended to include the 

 sedimentary period represented by 6,000 feet of strata, as shown on his 

 (Berkey's) columnar section. Observations in this field do not, however, 

 support the hypothesis. It has been found that, with the exception of the 

 Ogden quartzite, the sedimentary series is remarkably uniform through- 

 out the whole extent of the Uinta region. The absence of the Ogden 

 quartzite may be due to the presence of a land mass, the Uinta fold 

 being then in an incipient stage. The evidences of unconformity at 

 the base of the Carboniferous Weber quartzite are inconclusive, as, con- 

 trary to Berkey's observations, no basal conglomerate in this series was 

 noted in the Uinta area. Occasionally there is a small development of 

 shales, but the transition from the underlying limestone to quartzite is 

 usually through light gray fine-grained sandstones. 



The Tertiary overlaps all the older strata, including the great interior 

 quartzite series, reaching a maximum elevation of 10,000 to 11,000 feet. 



Structure 



in qeneral 



Eegarding the structure of the Uinta uplift, King (3, page 753) 

 makes the following summar}'^ statement : 



"It [the Uinta uplift] consists of a broad central plateau 150 miles long by 

 30 miles wide, in which there are slight sags and local undulations, but the 

 average dip of the strata is from the horizontal only up to 4 or 5 degrees. 

 This broad, flat-topped arch suddenly gives way along the north and south 

 edges to two distinct axes of flexure where the horizontal rocks bend over, 

 accompanied by distinct faulting at ailgles varyiog from 10 to 70 degrees. In 

 the Green Eiver canyon the southern line of flexure becomes immensely com- 

 plicated and develops three local anticliuals." 



Powell does not present a summary of his conclusions, but I have gath- 

 ered together the following : The Uinta mountains have been produced by 

 the degradation of a great upheaved block having its axis in an east-west 

 direction. The displacement is partly by faulting, partly by flexing. 



