VARIATIONS IN UPPER CRETACEOUS SEDIMENTATION 345 



ciently general to drain the sea from the whole region. A few examples 

 will suffice. 



In the Datil Mountain area of western New Mexico coal-bearing strata, 

 with a land flora, were deposited early in the Colorado epoch. These 

 were again covered by the sea, but near the close of the Colorado the 

 area again emerged and received a thick series of continental deposits^ 

 with many thin coals and numerous land plants. So far as the record 

 shows the sea never again invaded this particular area. Farther north in 

 New Mexico and in southwestern Colorado marine sedimentation was 

 continuous throughout the Colorado epoch, and it was not until later in 

 the Montana epoch, at the time represented by the Mesaverde formation, 

 that the land emerged sufficiently to support forest growth and permit 

 the formation of coal beds. It is true that the Mesaverde formation in- 

 cludes some marine strata, but it consists in large part of non-marine 

 beds deposited above sealevel. These continental deposits of the Mesa- 

 verde formation cover large areas in western Colorado, in eastern Utah', 

 and in southern Wyoming from the Laramie Plains westward. 



East of the mountains in Colorado and a part of Wyoming there was 

 no break in marine sedimentation^ in either the Colorado or the Montana 

 epoch. There is, however, some evidence of differential movement and 

 of locally derived sediments in both epochs. In the Colorado group a 

 sandstone is developed as the uppermost member of the Benton immedi- 

 ately beneath the limestone of the Niobrara. This sandstone at some 

 localities in Huerfano Park, southern Colorado, is 40 feet thick and con- 

 tains an abundant littoral fauna, which, like the sands in which it is 

 embedded, indicates a near-shore deposit. It is 20 feet thick in the 

 Arkansas Valley above Pueblo, and northward decreases to 3 or 4 feet in 

 northern Colorado. 



North of Denver, in Colorado, the ^middle and upper parts of the 

 Pierre shale contain a large proportion of marine sandstones (of which 

 the Hygiene sandstone member is an example). Lithologically these 

 sandstones resemble the sandstones of the Mesaverde formation in north- 

 western Colorado and in the Laramie Plains and other parts of southern 

 Wyoming, and as they occupy approximately the stratigraphic position 

 of the Mesaverde it is probable that their materials were derived from 

 the erosion of the same land-masses. Other areas of land in the Colorado 

 epoch are indicated by coal-bearing formations in the Harmony, Colob, 

 •and Kanab coal-fields of southern Utah, in northern Utah, at Coalville, 

 and in western Wyoming, in the important coal-bearing members "pEffie 



Tosslbly the local structural breaks described by Eldridge iu the Denver Basin are 

 an exception. See Monograph U. S. Geol. Survey, vol. 27, pp. 91-111. 



