Jan., 1912.] The A rnheim Formation. 43 > 



At Cobb Ferry, miles south of the mouth of the Red river, 

 only the upper third of the shaly part of the lower Arnheim is 

 exposed. The fine <2jraincd, blue limestones, with gasteropods, at 

 the top of this division forms a section about 4 feet thick. In 

 descending order this section consists of one foot of limestone, 

 two feet of sandy shale with several thin limestone layers, and one 

 foot of limestone, underlaid by the upper third of the characteristic 

 shaly section. The Oregonia division here appears practically 

 unfossiliferous. 



East of the reservoir, two and a half miles east of Richmond, 

 Kentucky, the shale bed fonning the major portion of the lower or 

 Sunset division of the Arnheim, is 11 feet thick. It is overlaid 

 by very fine grained blue limestone, one foot thick; thin layers, 

 poorly exposed, having a total thickness of two feet; and hard 

 dense limestone, two feet thick, probably forming the top of the 

 lower Arnheim division. The basal part of the Oregonia division 

 consists of very dark shaly rock, one foot thick. This is overlaid 

 by hard blue limestone, 4 feet thick, containing fossils; spalling 

 clay rock, two feet thick; and light colored clay, bluish or greenish 

 in tint, assumed to form the base of the Waynesville or the top of 

 the Arnheim section. According to this interpretation, the thick- 

 ness of the Oregonia division of the Arnheim here is about 7 feet. 



The light colored clay, which occurs at the top of the Arnheim 

 section east of Richmond, is seen also east of College Hill, where the 

 thickness of the Oregonia division is estimated at 11 feet. At 

 ^Merritts Ferry, there is a layer of light blue clay sixteen and a half 

 feet above the base of the Oregonia division. At Ophelia, four 

 miles north of Richmond, the light colored clay is 11 feet above the 

 base of the Oregonia division. These data suggest a local thin- 

 ning of the Oregonia division southward as far as Richmond, 

 accompanied by a diminution of its fossils content. 



North of Ophelia, only the upper part of the lower Arnheim 

 division is well exposed. The lower part of the exposure, 5 feet 

 thick, consists of rather shaly limestone. The immediately over- 

 lying part of the section, 4 feet thick, consisting of fine grained 

 limestone more or less interbedded with clay shale, is regarded as 

 fonning the top of the lower Arnheim. Two of the component 

 limestone layers contain small gasteropods. The lower part of 

 the Oregonia division, six and a half feet thick, consists of rubble 

 limestone, containing Platystrophia ponderosa, Leptaena rich- 

 mondensis, and Rhynchotrema dentata. This more fossiliferous 

 part of the section is overlaid by 4 feet of argillaceous strata 

 containing Stromatocerium in the lower half. 



Stromatocerium occurs in the upper half of the Oregonia divi- 

 sion also at Alerritts Ferry, at the mouth of the Red river. Here 

 it is found 9 feet above the base of this division, above the richly 

 fossiliferous horizon, and 7 feet below the top of the Arnheim. 



