COAL. 343 



the western half of the distance is occupied by the coal measures, which 

 <li]i to the NNW. 5 ' to 10°, occasionally returning to a horizontal position. 

 Only traces of coal seams appear along here, and it is possible that the 

 series entire is not present; on the other hand, the coal beds themselves 

 may have decreased in thickness. Beneath Marshall hake the strata are 

 horizontal, hut in a deeply cut ditch to the north they assume a south- 

 easterly dip of '{- to Ki°, with a general strike X. 30 E. Southeast of 

 the lake, in the gentle rise of the mesa, the coal measures dip northwest. 



Along here the Ostrea bed is traceable for several hundred feet; it also 

 appears Hat in the bottom of the lake basin, the two outcrops, except for 



surface debris, being doubtless continuous. < )n the eastern side of the 

 basin the northwesterly dip continues to the southern end of the depression, 

 but, as will be shown beyond, the rim here becomes somewhat irregular in 

 trend, and the trough itself is considerably modified. 



From the horizontal outcrop of the Ostrea bed in the center of the 

 Lake basin the measures rapidly steepen southward, entering the bluff 

 southwest of the lake with a strike of S. 30° \V. and a dip of 24° NW- 

 The outcrop of the coal measures in the western walls of the basin con- 

 stitutes the eastern rim of the Marshall coal area in this part of the held, 

 the sharper and deeper portions of the syncline now lying entirely to the 

 west, beneath the prairie uplands. The synclinal depression, except for 

 the modification of its southeastern lip, is here, doubtless, at its narrowest 

 point, since, at the head of a gulch entering the basin from the northwest, 

 the beils have a southeasterly dip of 25° to 35°, their strike being X. 60 E. 

 and the distance across the trough not over li miles. The coal measures 

 entering the steep slopes at the southwest corner of the basin pass through 

 the mesa, to again outcrop in the bluffs on the north side of a short 

 tributary of Coal Creek. Coal is here reported .'U feet thick, but the drift 

 is now closed, an outcrop of little promise alone showing. The strike is 

 approximately X. 60 c Iv, with a well-defined dip of about <J NW. A short 

 distance down the gulch, on the opposite side, the basal sandstones are 

 seen, while above the higher coal-measure sandstones outcrop, succeeded 

 in turn by the upper Laramie shales and ironstones. A strike X. 60* E.is 

 of frequent occurrence in this portion of the field, and indicates a general 

 change in direction for the southern end of the synclinal axis. 



