182 GEOLOGY OF THE EUREKA DISTBICT. 



characterized by a fauna which did not differ in any marked degree from 

 the underlying limestone of the Lower Coal-measures. 



The Upper Coal-measures indicate once more that a deeper sea swept 

 over the siliceous beds as the limestones of this upper horizon were laid 

 down over a wide area, presenting great uniformity in composition and 

 marine life. Of these overlying rocks we have only 500 feet at Eureka, 

 and with them the geological record of Paleozoic time comes to an end. 



From this recapitulation of the record of the Eureka rocks, it is evident 

 that they were laid down under very varying physical conditions. In its 

 broader outlines this sequence of strata may be correlated with the rocks 

 of the Great Basin stretching as far eastward as the Wasatch, with this 

 difference, that at Eureka there may be seen immense thicknesses of shal- 

 low water sediments derived from a continental area to the west, whereas 

 in going eastward evidences of deeper waters are met with, the material 

 being more uniform in character and deposited in a quieter sea. In the 

 latter rocks there is, so far as yet recognized, a marked absence of argil- 

 laceous and calcareous deposits enriched with plant remains and fresh- 

 water shells. 



Naturally, it is the siliceous formations that exhibit the greatest litho- 

 logical contrasts, and in going eastward from off-shore to deep-water de- 

 posits it seems highly probable that Cambrian quartzite in places approxi- 

 mates the Eureka quartzite in appearance, and may possibly have been 

 mistaken for it. In the same manner the widely deposited Weber formation 

 passes from the coarse conglomerate as represented at Eureka into fairly 

 uniform beds of quartzite or sandstone. Owing to its geological position 

 between the Upper and Lower Coal-measures, it becomes a comparatively 

 easy matter to correlate the Weber quartzite of Eureka and Agate Pass 

 with sandstones farther eastward or the Weber shales of still other localities. 

 Again, the Weber epoch, when composed of fine siliceous grains and car- 

 rying a considerable amount of calcareous material, may be difficult to sep- 

 arate from the overlying and underlying limestones. 



Paieontoiogicai Divisions. As already mentioned, the 30,000 feet of strata 

 have been divided into the four great periods of Paleozoic time, and at 

 Eureka they have again been subdivided into epochs mainly based upon 



