300 Rogers — Persistent Parting in a 



In this district the coal bed containing the parting marks 

 the base of the coal-bearing member of the Lance. The bed 

 is not regular in thickness and possibly not even continuous 

 throughout the area examined, but is made up of a number of 

 lenses* which range in extent up to 40 square miles or more. 

 It is probable that the vegetal matter was laid down in a series 

 of semi-independent swamps during approximately the same 

 period of time, a condition which has given rise to a series of 

 lenses which are at exactly or very nearly the same horizon. 

 It is not known whether these lenses are isolated or whether 

 they are connected by a thin layer of carbonaceous material 

 and therefore constitute one bed ; but it is certain that they are 

 all at the same stratigraphic horizon, and in this discussion 

 will therefore be treated as a unit. 



The strata above and below the bed also vary greatly in 

 character and thickness. The immediate roof and floor are 

 commonly carbonaceous shale, although bluish or greenish 

 shale or sandstone have been observed. About 10 feet above 

 the bed is a sandstone which is as much as 30 feet thick in 

 some localities and entirely absent in others. In some localities 

 there is a prominent sandstone underlain by greenish shale 

 from 10 to 40 feet below the bed ; in other places the bed is 

 directly underlain by the greenish shale and the sandstone is 

 absent. As stated above, the irregularity of the formation is 

 one of its most striking characteristics. 



Notwithstanding the lenticularity of the coal bed, it con- 

 tains a parting of almost constant thickness at every point at 

 which it was examined. The detailed examination was 

 restricted chiefly to the areas in which the bed is over 18 

 inches in thickness, but in some other localities the horizon 

 was used as a datum plane and much information concerning 

 it was thus collected. The parting almost invariably occurs in 

 the upper third of the bed and varies only slightly in thickness. 

 It averages f of an inch and is commonly between \ and \\ 

 inches in thickness. It is generally bordered by good clean 

 coal, although in places it is associated with impure coal or 

 bone. It persists even where the bed is very thin and gener- 

 ally maintains its characteristic thickness and position in the 

 bed. In one locality the bed is represented by only 2 inches 

 of bone but the parting is present and is about half an inch 

 thick. Its persistence and regularity are thus in striking con- 

 trast to the character of the rest of the bed and to the forma- 

 tion, a fact which induced the writer to examine it more 

 particularly in the office. 



Lithoiogy and composition. — The material of which this 

 parting is composed is granular and closely resembles a brown 



* In this examination, coal beds less than 18 inches in thickness were not 

 mapped ; the lenses referred to are therefore considered as delimited by the 

 line alone; which the coal is 18 inches thick. 



