1S97.] DKAKE — THE GEOLOGY OF IXDIAX TERRITORY. 349 



Boone Chert and Limestone. 



Stratigraphic Position. — Immediately above the Eureka shale, 

 there is a series of cherts and limestones aggregating from fifty to 

 about five hundred feet in thickness, and averaging about three 

 hundred and fifty feet. It was named the Boone chert by Dr. 

 Branner because of its extensive and typical development in Boone 

 county, Ark.^ These beds are the probable equivalents of the Bur- 

 lington-Keokuk divisions of the Lower Carboniferous. 



Areal Extetit. — The Boone chert and limestones form the prin- 

 cipal strata outcropping over several counties in southwest Missouri 

 and northwest Arkansas, and continue into the Territory, where 

 they cover half of the Cherokee Nation — three thousand square miles. 

 They lie in the northeastern and east central part of the Cherokee 

 Nation. Roughly, their western limit is four to five miles west of 

 Grand river and their southern limit some twenty to twenty-five 

 miles north of the Arkansas river. Tracing the boundary more 

 definitely, it enters the Territory south of Baxter Springs, Kans., 

 curves to the southwest, passing through Miami, thence bears 

 southward to near Fairland, whence it extends southwestward to a 

 point on the M. K. & T. Railway, some four or five miles south- 

 west of Vinita. From this point it runs southward in a wavy line 

 between the railway and Grand river to a point about fourteen miles 

 north of Ft. Gibson. From this point it runs eastward in a zigzag 

 way to a point about one and a half miles south of Tahlequah. Then 

 in its eastward course it swings southward, passing a little south of 

 Park Hill, makes deep southward swings on the Illinois river, Sali- 

 saw and Lee's creeks, and passes into Arkansas a little north of Evans- 

 ville. All along this border, and more especially its southern part, 

 there are small isolated areas of higher geologic horizons scattered 

 over the chert area along drainage divides. 



Structure. — Over most of this area the beds are practically hori- 

 zontal, but nearer the borders the strata dip toward and at right 

 angles to the border line. In the northwest part of the area this 

 dip, even along the border line, is barely perceptible, but toward 

 the south the dip increases and also becomes more irregular by the 

 increased folding and some faulting along several axes. These dis- 

 turbances largely account for the irregular border of the chert area 

 on the southwest and south. 



'^An. Rep. Geol. Stir. Ark., 1890, Vol. i, p. 129. 



