1881.] ^J-S [Stevenson. 



40 degrees, made raising tlie coal by liorse-power too difficult for profit. 

 The crushed outcrop at this pit shows a thickness of nearl}^ 20 inches, but 

 the bed is said to show 3 feet of good coal at the end of the slope. The 

 overlying shale is thin and is covered by a yellow sandstone. 



A low mound rises in the park between this ridge and the bluflF. A 

 coal blossom was seen here, but its place was not determined, though the 

 bed is probably C. The blossom indicates not much coal. 



Followed southward the yellow sandstone associated with Coal bed A is 

 seen foi'ming a sharp low ridge, which continues southward to the head of 

 Oak creek, where it is lost in the mesa. At the head of Oak creek caiion 

 a park intervenes between the bluflF and the sandstone ridge ; but south- 

 ward the park becomes narrow and at length the mesa and the low ridge 

 are united. An exposure on Mr. Bishop's ranch, near the point of union, 

 shows the following section : 



1. Coal bed a 0' 7" 



2., Shale and some sandstone 22' 



3. Coal bed B1 0' 2" 



4. Shale 36' 



5. Coal bed A 3' 10" 



6. Shales, sandy, not fullj' exposed 15' 



7. Deep yellow sandstone, estimated. 100' 



The identification of the smaller coals is only provisional, there being 

 no other detailed measurenlents on this side of the field for comparison.. 

 The coal of bed A appears to be by no means bad and the crop coal has a 

 bright fracture. The dip is vertical here and the bed can be followed 

 easily from this place to where it passes into the mesa. 



The sandstone below the coal is the lowest bed of the Coal group.- 

 The upper part is hard sandstone, honey- combed with films of quartz, and 

 holds thin beds or pockets of conglomerate in which the pebbles vary in 

 size from buckwheat to pea. The color varies from cream to deep reddish 

 yellow, and in most respects the rock is an almost exact duplicate of the 

 Dakota sandstone, which is exposed within a short distance at the foot of 

 the Greenhorn mountains. The lower part of the mass becomes more or 

 less shaly, and at length passes into a series of dull reddish shales, somewhat 

 sandy but mostly argillaceous, and showing little structure. These in 

 their turn pass almost imperceptiblj' into the Fort Pierre shales, which are 

 well exposed at the head of Oak creek, where they hold the customary 

 septaria and abundance of selenite. The thickness of the dull beds below 

 the sandstone was not measured on Oak creek, but it appears to be not far 

 from 100 feet, 



The Niobrara and Fort Benton groups are fairly well shown at the head 

 of the creek and as far down as Mr. Bishop's ranch ; but no effort was- 

 made to determine their thickness. The Dakota is exposed on a tributary 

 of Oak creek, where it is said to contain a thin bed of fairly good coaK 

 This has been opened and the whole space underlaid by the Dakota has 

 been taken up as coal land. The guide was unable to find the opening,. 



PROC. AMER. PHILOS. SOC. XIX. 109. 3jr. PRINTED DEC. 5, 1881. 



