MEDIAEVAL OR MESOZOIC TIMES. 207 



throughout the whole 12,000 feet, they recur in that region. They 

 increase in frequency after the close of the Fox Hills Group, and 

 are most abundant through the 4,000 or 5,000 feet of the closing or 

 Laramie Group of the series." In illustration of this statement, it 

 is reported by Emmbns that a bed of coal ten feet thick, of excel- 

 lent quality, is located south of the Uinta at Ashley Creek, in the 

 Dakota Group. Of equal excellence is another bed of coal of equal 

 thickness in the Fort Benton Group, higher up in the series, but 

 near the same place. Another thick coal bed, on the south side of 

 the Uintas, is reported by Marsh, in the Niobrara Group. Coal 

 is also reported in workable quantities in the Fort Pierre, and in 

 still larger quantities in the Fox Hills Group. The inference, 

 therefore, is legitimate that there were betimes, during the progress 

 of the Cretaceous Age, extended land surfaces in this region, fol- 

 lowed by subsidences. 



Were there such subsidences and land surfaces in Nebraska dur- 

 ing this period? Thus far none to the same extent have been 

 found. At a few places in the Dakota Group, and also in the Fort 

 Benton, thin beds of lignite have been found. The thickest, thus 

 far, have been observed in Dakota and Dixon counties, where they 

 range from six to sixteen inches, but the lignite coal is of inferior 

 quality. As the strata are almost horizontal, and few canyons cut 

 through them, their study in Nebraska, in the absence of borings, 

 is difficult. It is possible, though hardly probable, that at some 

 points in our extended territory there may be basins of coal of good 

 quality in these deposits. Even in the mountains, the thick beds 

 occupy depressions in the strata, and soon thin out, only to increase 

 again in thickness farther on. To settle this question in Nebraska 

 definitely, will require many borings, over a large area of our ter- 

 ritory. One of the most favorable regions for testing for these 

 lignite coals is in northern and northwestern Nebraska. 



CLOSE OF THE CRETACEOUS AND TRANSITION PERIODS. 



With the close of the Laramie epoch, the whole series of con- . 

 formable strata, which had commenced with the Dakota Groups 

 ceased. When the last sediments of the Laramie Group had been 

 laid down, there occurred one of the great geological revolutions in 

 the history of the globe. Frorn the eastern base of the mountains 

 to the Wasatch, the whole region was thrown into a series of folds, 

 and undulations. The Uinta Range, with its broad, flat anticlinal, 



