MINING DISTEICTS. 9 



although, in one instance, a relic of land vegetation is imbedded with them. 

 We look in vain for any evidences of shallow areas ; the whole Carboniferous 

 zone is of fine homogeneous materials, deposited with rare regularity, and 

 without a single evidence of cross-currents, or any appearance of wave-marks. 



The two bordering systems contain, however, near the upper limits of the 

 Cretaceous and upward into the Tertiary, important beds of coal. The exact 

 age of this coal has been long discussed, authorities differing. It seems prob- 

 able, from the discoveries of this Exploration, that both parties are grounded 

 in fact. 



Of the Cretaceous origin of the California beds. Professor J. D. Whitney 

 is certain, and the writer has, as will be seen in a later chapter, shown the 

 same age for those beds which are included in the sandstones along the east 

 base of the Wahsatch Chain. Continuing eastward, the strata, still remaining 

 conformable, undergo a change of character. The marine fossils disappear, to 

 be replaced, first, by brackish-water types of doubtful affinities, and finally by 

 clearly recognized fresh-water Tertiary forms, the coal beds continuing at 

 intervals through this transition period. Dr. Hay den is unquestionably right 

 in assigning a Tertiary age to many of the beds east of Green River; so that, 

 as is often the case, the contestants for both views are correct in their 

 data. 



