UNCONFORMITY OF TERTIARY AND CRETACEOUS. 



157 



tory of the unconformity is clearly revealed. The monoclinal involves the 

 whole Cretaceous system, but not the overlying Tertiary, and fixes the age 

 of the disturbance between the close of the Laramie and the beginning of 

 the Tertiary. The northern extension of the Water-Pocket flexure indi- 

 cates a precisely similar movement coeval with the one already recited. 

 This flexure disappears beneath volcanic accumulations at Thousand Lake 

 Mountain. The summit of that mass consists of lava-capped Tertiary 

 strata resting upon the Jurassic, while to the northeast of the mountain the 

 Cretaceous beds are rolled up towards it monoclinally, with patches of 

 level Eocene beds lying unconformably across their edges. An uncon- 

 formity of Tertiary and Cretaceous is also laid open to view in Salina 

 Canon. Around the flanks of the Markagunt Plateau many exposures of 

 this unconformity are also seen. In truth, there appears to have been at 

 this epoch a series of displacements having a north and south trend, break- 

 ing up the Mesozoic system into long blocks by well-defined monoclinal 

 flexures, and the uplifted portions everywhere sufiered denudation prior to 

 the deposition of the Tertiary beds. On the other hand, very many of the 

 contacts of the Eocene and Laramie beds are apparently conformable. 

 This occurs wherever the older series escaped distortion, and throughout 

 the central parts of the Plateau Province they usually did escape it. The 

 great disturbances were for the most part localized in the vicinity of the old 

 shore line, and only now and then extended far away from it. The dis- 

 turbances, being also chiefly monoclinal flexures and faults, did not disturb 

 very noticeably the horizontality of the strata except along the very narrow 

 locus of the flexure itself 



The existence of these unconformities indicates a lapse of time between 

 the close of the period of deposition of the Laramie beds and the begin- 

 ning of the local Eocene. Nor could this period have been of very trifling 

 duration, for there are instances of extensive erosion of the Upper Cre- 

 taceous prior to the deposition of the earliest Tertiary. In the Aquarius 

 Plateau and in Thousand Lake Mountain the Lower Eocene rests upon the 

 Jurassic, and in the southern amphitheaters of the Aquarius the Tertiary 

 -lies across the beveled edges of the whole Cretaceous system. Whether 

 such an occurrence may be construed as meaning a temporary emergence 



