Jan., 1912.] The Arnheim Formation. 435 



argillaceous limestone section containing few fossils, although 

 occasional specimens of Platystropkia ponderosa are found. The 

 shaly layers and the dove colored limestone are absent. Platys- 

 tropkia ponderosa 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 Plalystrophia 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 south west 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 

 are 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 HeberteUa, 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. 



