Jan., 1912.] 
The Arnheim Formation. 
435 
argillaceous limestone section containing few fossils, although 
occasional specimens of Platystrophia ponder osa are found. The 
shaly layers and the dove colored limestone are absent. Platys- 
trophia ponder osa is not abundant in the upper Arnheim at any 
horizon, but specimens occur in moderate quantities at the base 
of this upper division. The exact horizon of the various fossils 
has' not been worked out in all of this territory, but at Maysville, 
and northward, the Platystrophia ponderosa horizon is below, not 
above, the horizons containing Leptaena richmondensis and 
Rhynchotrema dentata. 
3. Central Kentucky, from Stanford to Lebanon. 
The most western locality in Lincoln county at which Leptaena 
richmondensis at present is known from the Arnheim is found by 
going from the center of Stanford three-quarters of a mile south- 
ward and then the same distance southwest ward. The nearest 
point at which Rhynchotrema dentata is known, is four miles 
northeast of Stanford, three-quarters of a mile directly south of 
Gilbert Creek station. West of these localities there is a gap of 
14 miles within which no specimens of Leptaena or Rhynchotrema 
arc known in the Arnheim. Within this gap it has been found 
difficult to assign definite limits between the upper and lower 
divisions of the Arnheim, although a few data are known which 
may prove of assistance. 
At the locality a mile and a quarter southwest of Stanford, 
already mentioned, it is possible to identify the light colored clay 
with bryozoans, at the top of the Arnheim; the richly fossiliferous 
zone containing Platystrophia ponderosa and forming the lower 
part of the upper or Oregonia division of the Arnheim; and the 
Leptaena richmondensis horizon at the base of this division. At 
the top of the lower or Sunset division of the Arnheim, dove 
colored limestones occur, and these contain a globular bryozoan, 
which has been called Prasopora in the field. 
This globular bryozoan occurs three and a half miles southwest 
of Stanford, a mile south of the Turnersville pike, east of the former 
site of a creamery at the home of Katie Ador. Here the globular 
bryozoan is fairly common in massive argillaceous rock, 4 feet 
thick. The layers with Hebertella, and a species of Platystrophia 
near PI. clarksvillensis, are regarded as equivalent to the light 
colored clay layer at the top of the Arnheim. It was not possible 
to assign a definite limit to the base of the Arnheim. 
The same globular bryozoan occurs also on the hill northwest 
of McKinney; in the railroad cut south of Moreland; and north of 
Knob Lick branch, a mile south of Shelby City station. The 
significance of this globular bryozoan horizon can be best under- 
stood after an examination of some of the sections still farther 
west, at which Leptaena and Rhynchotrema again occur at the 
Arnheim horizon. 
