Jan., 1912.] 
Ihe Arnheim Formation. 
441 
Lithologically, the rock from the creek level as far up as the 
argillaceous rubble limestone above the highest Leptaena horizon 
resembles the rock forming the Mount Auburn member in most of 
Ohio and adjacent Kentucky. Moreover, there is a considerable 
interval between this part of the section and the Dinorthis carleyi 
horizon. However, Leptaena richmondensis is unknown in the 
Mount Auburn member from any of the numerous exposures 
where this horizon has been definitely identified. Hence, the 
Collinsville section may be merely an Arnheim exposure in which 
the interval between the Platystrophia ponderosa horizon and the 
Dinorthis carleyi horizon is represented by an unusual thickness 
of strata. 
As a rule, Leptaena richmondensis occurs in the Arnheim of 
Ohio only a short distance below the Dinorthis carleyi horizon. 
The interval rarely exceeds five feet, and frequently is reduced to 
only a few inches. 
At the Blacksmith hollow, a short distance north of the railroad 
station, at Oregonia, Ohio, six miles northeast of Lebanon, the 
following section is seen : 
Massive nodular argillaceous limestone oft. 6 in. 
One specimen of Strophomena concordensis. 
Rubble clay rock with some argillaceous limestone 15 ft. 
Dinorthis carleyi common 6 in. 
Rubble clay rock with Dinorthis at various intervals 5 ft. 
Rubble clay rock with Rafinesquina 1 ft. 
Dinorthis carleyi common and one specimen of Leptaena 
richmondensis in thin limestone. 
Interval 9 in. 
Dinorthis carleyi, one specimen. 
Leptaena richmondensis common 1ft. 6 in. 
Rubble clay 1ft. 6 in. 
Platystrophia ponderosa rare. 
Rubble clay rock, with Cyclonema humerosum, Rafinesquina 
loxorhytis, and Zygospira modesta 12 ft. 
Interval not exposed 17 ft. 
Estimated level of base of Arnheim. No exposures here. 
A similar succession of strata is found near the home of G. W. 
Robertson, at the mouth of Lick run, opposite the mouth of 
Caesar creek, less than three miles north of Oregonia: 
Nodular limestone, forming small falls. 
Interval loft. 6 in. 
Dinorthis carleyi at various intervals 6 ft. 
Leptaena richmondensis common Gin. 
Interval 3 ft. 6 in. 
Strongly wave marked limestone layer, trend of ridges about 
north and south. 
Interval 3 ft. 
Platystrophia ponderosa rather common 4 in. 
A similar succession of strata is seen three miles northeast of 
Goshen, at the middle part of the northern edge of Clermont 
