328 THE CAMBRIAN. [bull. 81. 



r£sum6. 



The sedimentation of the western area is uinch more varied and 

 larger than that of the eastern side of the Rocky Mountains. The 

 southern portion, represented by the Eureka District section, extend- 

 ing from the basal quartzite to the base of the Lower Silurian (Ordovi- 

 cian), is a continuous conformable succession of limestones and cal- 

 careous shales, with the exception of a narrow belt of arenaceous 

 shales resting directly upon the lower quartzite. The calcareous sedi- 

 ments are 6,200 feet in thickness and include the faunas of the Middle 

 and Upper Cambrian. The Lower Cambrian fauna is well developed 

 in the shales between the limestone and the quartzite. The Highland 

 Range section, 125 miles to the south, has a thickness of 4,800 feet of 

 limestone, between the quartzite and the Lower Silurian (Ordovician). 

 Proceeding eastward from central Nevada to northern central Utah, 

 the Cambrian formations thin out, and on the flanks of the Wasatch 

 Mountains are represented by 250 feet of argillaceous and siliceous 

 shales above the basal quartzite. In this section only the Lower and 

 Middle Cambrian faunas are found. The three thousand or more feet 

 of limestone, with an abundant Upper Cambrian fauna, found in central 

 Nevada, is unrepresented. 



A comparison of the section in the Wasatch Mountains with that of 

 Nevada shows that in both the earlier conditions of sedimentation 

 were apparently the same. But during the deposition of the Upper 

 and Middle Cambrian rocks, in the immediate vicinity of the Wasatch 

 Range, it was an area of minimum deposition of argillaceous sediment, 

 while that of Central Nevada was one of a great accumulation of calca- 

 reous sediment. 



What the conditions were in the vicinity of the Wasatch Range 

 during the deposition of the great calcareous deposits of central Nevada 

 of Upper and Middle Cambrian times is largely conjectural. The 

 physical appearance of the rocks indicates a shallow sea with very 

 little deposition of sediment during the earlier portion of Cambrian 

 time, and either a very shallow sea without deposition of sediment or 

 a very deep sea without deposition of sediment, during the latter part 

 of Cambrian time. It may be that some sediment was deposited and 

 subsequently was removed by erosion, but this is exceedingly doubtful. 

 The pure limestones of the Lower Silurian (Ordovician) rest directly 

 upon the shales of the Cambrian, without any apparent unconformity. 



To the north, near Malade City, Idaho, there are 1,200 to 1,400 feet 

 of limestones that occur above the series of quartzites and slates. The 

 sedimentation is essentially the same as that of central Nevada wi;h 

 the exception of a less amount of calcareous sediment above the basal 

 quartzite. The Upper Cambrian fauna has been found, but not the 

 Middle or Lower fauna. Still farther to the north, in western Alberta, 

 and eastern British Columbia, the same series is represented iu the Bow 



