THE MORRISON FORMATION OF COLORADO 345 



most conspicuous part of the canyon walls. It is notably cross- 

 bedded and the frequent changes in the direction of bedding, as 

 well as the frequent truncations of the cross-bedded layers, is 

 indicative of deposition by shifting currents. The upper part of 

 the massive series is slightly calcareous and oolitic, the little 

 spheres of which, about one millimeter in diameter, are harder 

 than the matrix in which they are set, and the weathered surface 

 is thus given a "bird's-eye" appearance. The oolitic beds pass 

 gradually upward into gypsiferous shales and thence into solid 

 gypsum without anv indication of stratigraphic break or lapse of 

 time. No trace of fossils of any kind was found in the Red 

 Beds. 



The upper sandstone forms the general surface of the 

 country over wide areas. The Cretaceous formations from the 

 Ft. Pierre to the Dakota are traversed in passing eastward from 

 Trinidad across the El Moro quadrangle which has been de- 

 scribed by R. C. Hills, 1 and the Dakota, may be traced onward 

 thence over the whole region studied. The Dakota is com- 

 posed mainly of sandstones, although shales occur in it in places. 

 About 150 feet from the base occurs a steel-blue shale (prob- 

 ably fire-clay) , 2 to 6 feet thick were examined. Above this 

 clay the formation is somewhat evenly bedded, ripple-marked 

 and in certain places contains numerous impressions of dicoty- 

 ledonous leaves. In a few places small pebbles were found 

 near the base. The largest of these were about one fourth inch 

 in. diameter. The pebbles are so few in number that the strata 

 containing them can scarcely be described as conglomeratic. 



Between the Dakota and the gypsum at the top of the Red 

 Beds lies the shale formation under consideration. It is constant 

 in occurrence, although the thickness varies from place to place. 

 At the mouth of Plum Canyon the thickness is 85 feet; in Red 

 Rocks Canyon, it is 132 feet. In Chaquaqua Canyon, ten miles 

 from the mouth of Plum Canyon, it is 175 feet (by barometer). 

 The formation is composed mainly of variegated clay-shales of 

 the variety known as "joint clay." A subordinate amount of 



1 U. S. Geol. Surv., El Moro Folio, Colo. 



