158 The Ohio Journal of Science [Vol. XVI, No. 4^ 



buff stone in this particular exposure is the almost complete 

 absence of carbon lines, which causes it to stand out in strong 

 contrast to the gray stone with its profusion of these lines. 



Third. — Throughout the buff stone of this particular 

 exposure, but especially numerous in its heavier lower ledges, 

 occur "cup and cone concretions." These peculiar forms are 

 fully treated in another paper, but for the present study the 

 cavity usually present with them affords the best place for the 

 collection of carbonaceous material. These "concretions" 

 do not occur in the gray stone, and it seems that the looser 

 texture of the buff stone favors their formation. 



From the rock surrounding the cavities the carbonaceous 

 material drains into them. Here the natural "rock tar" is 

 found. Sometimes it spreads out and fills the cavity; sometimes 

 it adheres to the walls of the cavity in drops as large as the end 

 of the little finger. This is pure, solid carbon material, hardened 

 and brittle; when heated it becomes waxy and burns with a 

 heavy, oily flame. While a rare form, Figure No. 3 admirably 

 illustrates how this collection does take place. The drop in the 

 cavity at the termination of a carbon line along which has 

 been the flow is conclusive evidence. Also on the sides of the 

 "cup and cone concretions" are lines of fracture where car- 

 bonaceous material accumulates. Here it appears in streaks. 



Summary. — The Greenfield member of the Monroe for- 

 mation contains much carbonaceous material, evidenced by 

 odor, carbon sheets and lines, carbon stains, and solidified 

 "rock tar." Its close texture prevents that accumulation 

 necessary for a paying gas or oil rock. If its texture were open 

 and spongy then it might have had economic value other 

 than that for building and agricultural purposes. 



EXPLANATION OF PLATE. 



Fig. I. Occurrence of carbonaceous material in gray stone. "Carbon 

 sheets" occur between layers nearest contact with buff stone in which they are 

 far more numerous. "Carljon lines" are profuse throughout the gray stone and 

 serve to distinguish it. 



Fig. 2. Occurrence of carbonaceous material in buff stone. Upper layer 

 stained with carbon material; lower layer to show collection in cavities and in 

 "cup and cone" concretions. 



Fk;. 3. "Rock tar" in buff stone. Collection and How liave been along 

 carbrm line, terminating in carbon drop in cavity. 



