Jan., 1912.] 
The Arnheim Formation. 
43 5 
At Cobb Ferry, 6 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 grained, 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 forming the major portion of the lower or 
Sunset division of the Arnheim, is 1 1 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 1 1 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- 
hung part of the section, 4 feet thick, consisting of fine grained 
limestone more or less interbedded with clay shale, is regarded as 
forming 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 Merritts 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. 
