43^6 The Ohio Naturalist. [Vol. XII, No. 3, 



One of the most instructive sections in this connection is that 

 exposed along the lower part of Walloway creek, opposite the home 

 of J. W. Isaacs, in Marion county. The locality may be reached 

 by going one mile west of Rileys station and then following a road 

 southward almost two miles. The section is described in descend- 

 ing order. 



Argillaceous nodules and globular bryozoan 1 ft. 10 in. 



Interval with various fossils 3 ft. 6 in. 



Richly fossiliferous horizon with Platystrophia ponderosa 6ft. Gin. 



Leptaena richmondensis at various levels, Ijut rare except at base. 5 ft. 6 in. 



Argillaceous limestone, fossils few 3 ft. 6 in. 



Large branching bryozoans resembling Batostoma 1 ft. 



Same large bryozoans and the globular bryozoans resembling 



Prasopora 6 in. 



Argillaceous limestone with the same large branching bryozoans 1 ft. 



Argillaceous rock, fossils few 3 ft. 



Dove colored limestone with Platystrophia ponderosa 5 ft. 



Opposite home of J. F. Crews, remainder of section down stream 



not visited. 



In this section, the Leptaena horizon is regarded as the base 

 of the upper or Oregonia division of the Arnheim. Globular 

 bryozoans occur at two horizons ; at the top of the Arnheim section, 

 associated with argillaceous nodules; and a short distance below 

 the Leptaena horizon in strata which may belong to the lower 

 division of the Arnheim but whose exact stratigraphical equivalent 

 can be determined only after further study. It is possible, for 

 instance, that the lower Arnheim practicall}' thins out west of 

 Stanford. The two horizons for the Prasopora usualh' may be 

 distinguished readily. At the upper horizon, argillaceous nodules 

 frequently are present, and both the globular bryozoans and the 

 nodules occur in a whitish or light colored clay which is regarded 

 as the stratigraphical equivalent of the light colored clay at the 

 base of the Waynesville section northeast of Stanford as far as the 

 mouth of the Red river. This liorizon is always above the highest 

 layers containing Platystrophia ponderosa. The lower horizon 

 with the globular bryozoan occurs at the top of a section consisting 

 of dove colored limestones and usually is overlaid by a small 

 section of strata containing Platystrophia ponderosa. Near the 

 base of this upper Platystrophia ponderosa horizon, Leptaena 

 richmondensis and Rhynchotrema dentata occur at numerous 

 localities, but where the latter species arc fotmd, the globular 

 bryozoan is not needed as a horizon marker. 



The globular bryozoan has a fair distribution at both the 

 upper and the lower horizon. At the upper horizon it occurs 

 from the vicinity of Lebanon as far east as Scrubgrass creek 

 southwest of Mitchellsburg in Boyle county, and a mile east of 

 Harveyton, in Casey county. Southward it is known as far as 

 Rush Branch, in the southeastern corner of Marion county. At 

 the lower horizon, it is known at numerous localities southwest of 



