24 i Re ANNUAL REPORT 
This shows that the two formations are about 400 feet apart, and 
as has already been stated, the interval is occupied by the Berea and 
Cuyahoga shales. 
The Logan group, as classified by Orton, consists of three mem- 
bers—a conglomerate, sandstone and shale—and has a maximum thick- 
ness of 350 feet.’ Quite recently, however, Professor Prosser has con- 
sidered the question, and he divides the group as follows: . 
2. Logan formation —TJ.ogan sandstone and shales. 
1. Black Hand Formation = Logan conglomerate. 
The Big Injun series is limited above by the Lower Carboniferous 
or Maxville limestone, which in Monroe, the southeastern corner of 
Belmont and the eastern part of Washington counties is kuown as the 
Mountain limestone, or, popularly with the driller,,as the “Big lime.” 
Outside of the two counties just named, however, this limestone is not 
reported, and hence the. upper limit of the Big Injun is not so well 
marked. In fact, over a large part of eastern Ohio, this formation and 
the Salt sand are confused. by the driller, who ADEN the latter name to 
the Big Injun. 
Above drainage He eroup is bo ciie ravieeah Hills capped with sand- 
stone 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 sand- 
stone 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. : : an 
Under cover the Logan group. inaevaseds important. charwes! and 
the several formations are given different names from those at the sur- 
face. Thus, instead of the Logan conglomerate, sandstone and shale, we 
have the Keener, Big Injun and Squaw sands. 
The Mountain limestone has been shown by paleontological evidence 
to be the equivalent of the Maxville or Subcarboniferous limestone. The 
formation is known in West Virginia as the Greenbrier limestone. In 
Ohio it has a maximum thickness of 110 feet. It is a light-colored, 
hard, massive rock, free from oil and gas except along its margin, where 
the formation becomes broken and the layers of limestone are intercalated 
with sandstone. The formation is wedge-shaped, with the apex to the 
northwest. It is limited to the eastern half of Washington and Monroe 
1Geol. Survey of Ohio, Vol. VII, p. 32. 
2Journal of Geology, Vol. IX, p. 215. 
