THE OIL- AND GAS-PRODUCING ROCKS OF OHIO 831 



Putnam Hill limestone 

 Lower Carboniferous limestone 

 Salt sand 

 Berea shale 

 Berea grit 



top at 20 feet, 



bottom at 23 

 top at 225 



bottom at 265 

 top at 450 



bottom at 485 

 top at 919 



bottom at 952 

 top at 950 



bottom at 980 



( top at 980 



Bedford shales (brick red) - •< . 



v ( bottom at 1,010 



Ohio shales, top at - - - - - 1,010 

 This shows that the Salt sand lies 185 feet below the Lower 

 Carboniferous limestone. Combining this with the record of the 

 Mead well previously given makes a total thickness for the 

 Logan group of 715 feet. Probably in the extreme southeastern 

 corner of the state the thickness is still greater. 



Above drainage the group is well marked. Hills capped 

 with sandstone or conglomerate stand out in bold relief, so that 

 the limits of the formation are discernible from a distance. The 

 conglomerate is the most conspicuous member of the group, It 

 is essentially a quartz rock, the largest pebbles of which do not 

 commonly exceed one-half of an inch in diameter. It is the 

 best known bridge stone in the state. The sandstone member 

 has usually a yellow or brown color, but sometimes this becomes 

 strikingly variegated. It is extensively used for building pur- 

 poses. The members of this group are much less constant in 

 their physical characters than the Berea grit, and hence their 

 identification is correspondingly more difficult. 



Under cover the Logan group undergoes important changes, 

 and the several formations are given different names from those 

 at the surface. Thus, instead of the Logan conglomerate, sand- 

 stone, and shale, we have the Big Injun sand, Mountain lime- 

 stone, Salt sand, etc. The correlation of the strata bearing these 

 two sets of names is as follows. This is based on their strati- 

 graphical succession and lithology. While the limits under- 

 ground cannot be sharply drawn in most cases, they are perhaps 

 as definite as those along the line of outcrop. 



