PALEOZOIC STRATIGRAPHY OF ROCKY MOUNTAINS 389 



received any notable quantity of arenaceous sediment, so far as the 

 record now shows. During long intervals the deposits accumulat- 

 ing on the floor of the clear sea which covered this area were nearly 

 or quite without clastic ingredients. At no time was clastic mud 

 brought in in such quantity as greatly to preponderate over cal- 

 careous matter. This condition makes it certain that there were 

 no high shores, nor debouchures of streams draining areas of high 

 relief or dry climate, in or very near to the region under consid- 

 eration. 



Evidence that the sea was shallow. — The intraformational con- 

 glomerates which characterize the upper part of the Upper Cam- 

 brian and much of the Beekmantown series record the fact that the 

 seas of that time were shallow enough to permit the breaking and 

 movement, by waves or currents, of freshly or partly consolidated 

 sediments on the sea bottom. 



The Chazyan{?) sands. — -Somewhat later in the Ordovician 

 period, probably in the Chazyan epoch, a flood of sand swept over 

 the extreme northern part of Utah and much of eastern Nevada 

 (see Fig. 8). This was probably the result of an uplift of neigh- 

 boring lands, perhaps in central or eastern Utah. 



Emergence and peneplanation. — Subsequently, the entire region 

 shown in the accompanying maps (Figs. 6-10, 12, 13) emerged and 

 the freshly exposed sediments were subjected to extensive erosion, 

 which continued until about the close of the Black River epoch. 

 This emergence took place without any appreciable deformation of 

 the Cambrian and early Ordovician sediments. Probably it pro- 

 duced no great relief in the region where those sediments are known. 

 The first deposits of the succeeding submergence were laid down on 

 a surface whose relief probably did not exceed 200 feet in all north- 

 ern and western Wyoming, and on which, in that region, slopes 

 as steep as io° were, so far as known, nowhere more than a few feet 

 or yards in length. Either the relief was not greater than this at 

 any time during the interval of emergence or a rougher surface was 

 reduced to this condition by stream erosion during that interval, 

 with the aid of marine planation at the border of the advancing 

 Middle Ordovician sea. 



