Part I. Introduction: Region and Rocks Studied
Certain aspects of this report touch upon the stratigraphy throughout most of the lower Mississippian outcrop areas of the east-central interior of the United States, but the region of special field study by the writer is that which stretches from Fountain County, west-central Indiana, south-southeastward through southern Indiana into Kentucky, thence southeastward, eastward, and northeastward around the margin of the Lexington Plain of Kentucky. The belt of outcrop continues thence northward across Ohio from Adams and Scioto counties at the Ohio River on the south to Erie, Lorain, Cuyahoga, Geauga, and Ashtabula counties bordering Lake Erie on the north (Pl. 1). This continuous, horseshoe-shaped outcrop belt has a length of approximately 700 miles. However, only the 450-mile portion through Indiana and Kentucky has been the object of detailed field observation.
The rocks for primary consideration are those of early Mississippian age, largely clastic, which lie generally between the “black shales” beneath and the Warsaw or younger rocks (usually limestones) above. They are regarded essentially, although not entirely, as a series of Osage age (Pl. 6). In Indiana the rock group is called the “Borden,” an appropriate name proposed by Cumings (1922, p. 487) to replace the older term “Knobstone.” Immediately underlying this thick group, in Indiana, is the thin Rockford (Kinderhook) limestone, which in turn rests upon the controtroversial New Albany “black shale.” The group is overlain by the Harrodsburg limestone which has been subdivided into “lower” and “upper” divisions. The first is . . .