298 S. P. EMMONS UINTA MOUNTAINS 



east, as Mr Berkey himself remarks, the Ogden quartzite is in juxtaposi- 

 tion to the Uinta quartzite and perfectly conformable in angle, and on 

 Rhodes spur, where the former caps a bold escarpment facing north, 

 overlooking the interior plateau, the shales are effectually concealed by a 

 talus of huge blocks of greenish white Ogden quartzite, likewise con- 

 formable. ^:n.^ 



Above the Wasatcli series is a great siliceous member consisting largely 

 of white calcareous sandstones and gray quartzites, which I correlate 

 with the Weber quartzite,* and for which Mr Weeks estimates an aggre- 

 gate thickness of 2,300 to 2,700 feet. 



This is presumably the series of beds at the base of which Mr Berkey 

 placed his main unconformity; but in spite of a most careful search, 

 continued by Mr Weeks throughout his circuit of the range, we were 

 unable to find the basal conglomerate on which Berkey's scheme of corre- 

 lation is mainly based. Negative evidence is confessedly somewhat dan- 

 gerous ground upon which to deny the existence of an unconformity by 

 erosion, since such unconformity involves no discrepancy of angle, and 

 the positive evidence of overlap is not necessarily present, while it is 

 rare, even in long and well exposed canyon sections, to get unmistakable 

 evidence of the unevenness of an old eroded surface in the hollows of 

 which the later beds were deposited. In the present case their superior 

 resistance to erosion and the slowly steepening angle of dip have com- 

 bined to leave patches of the Weber beds in abnormally high positions on 

 the spurs (see map, figure 2), which probably led Mr Berkey to suppose 

 they came there by overlap. Even did such an unconformity exist, how- 

 ever, his scheme of correlation based on it would fail, since it assume;: 

 that it is the same unconformity that Powell observed in the canyon of 

 Green river; but there the Bed Wall limestone, which corresponds to the 

 Wasatch of the Duchesne, lies above this unconformity. Even Mr Be^- 

 key's hypothesis of a sea that was slowly retreating westward and then 

 rapidly readvaneing could hardly account for the same beds being de- 

 posited above the erosion interval in one place and below it in another. 



Above the Weber quartzites are cherty limestones, followed by cal- 

 careous sandstones and argillaceous shales, in which the calcareous ele- 

 ment decreases upward until they end in a series of deep red shaly beds 

 which, owing to their easy erosion, are apt to form hogback valleys. 



* It has been considered advisable to use tlie old Fortieth Parallel names of forma- 

 tions and not attempt to make subdivisions characterized by local names until the 

 region is areally surveyed. For the great central quartzite series Powell's name, Uinta, 

 has been retained, because it is not only the most appropriate, but also possesses priority 

 in published description. As used on the Fortieth Parallel maps, this name indicated simply 

 an area of Tertiary beds of probable different ages, but not yet differentiated. 



