454 MINING INDUSTEY. 



mud rocks of the coal series. In the basin of the Uintah, which lies south 

 of this range, the parties of this Survey penetrated but a short distance, yet 

 their explorations were sufficient to develop the fact that the coal strata 

 were present over a very large area, extending indefinitely southward and 

 east. The thickness of the Cretaceous formation is as great as that north of 

 the range. Since, however, no roads penetrated this region, it must be a 

 very long time before settlements shall be founded there, and consequently 

 the coal strata were not studied in great detail. 



Subsequent to the laying down of the whole Cretaceous system, and of 

 those conformable fresh- water beds which close the coal-bearing period, 

 another era of mountain uplifts occurred, folding the coal series into broad, 

 undulating ridges, having a general trend of northeast. From evidence here- 

 after to be assembled it is clearly shown that the coal series were still sub- 

 merged beneath the fresh-water lake when the mountain uplift took place, 

 and that upon the flanks and summits of this series of northeast Cretaceous- 

 Tertiary mountain chains was deposited an unconformable sediment, which 

 gradually filled all the anticliiials, and at last buried the whole folded system 

 beneath an immense accumulation of horizontal sand and clay beds; 



In connection with the period of volcanic outbursts which were subse- 

 quent to the laying down of these latest horizontal strata, a third orographic 

 cal throe took place, which lifted the fresh-water horizontal beds, tilting 

 them to an angle of 15° to 20°, and throwing them into broad and gentle 

 undulations wherever they lay in the neighborhood of the older ranges, such 

 as the Wahsatch and Uintah. Shortly after the volcanic period, the Grreen 

 River Basin became drained, and a net-work of river svstems defined itself 

 down to the center, focusing in the Green River, which longitudinally drains 

 the whole elliptical basin. Erosion thereafter carved away a vast amount of 

 the uppermost Tertiary series, laying bare the undulating folds of the coal 

 rocks. 



When the topographical maps of this Survey are completed, the minute 

 details of the Cretaceous folds and of the fragmentary mass of the overlying 

 Tertiaries, which erosion has left upon their flanks and summits, will be 

 carefully laid down. For the present purpose, however, it is only necessary 

 to indicate the main outlines and geographical distribution of three rock sys- 



