«/. C. Branner — Paleozoic Sediments in Arhansas. 231 



The fossils found in the Eureka shale in Arkansas are mostly 

 Discinas and Lingulas and are of but little use in correlation, 

 but inasmuch as crinoid stems are abundant in places, and as 

 the shale merges gradually into the overlying Carboniferous 

 limestones, I am inclined to believe that it belongs with the 

 Carboniferous rocks. 



The Sylamore sandstone (one of the phosphate beds of 

 Arkansas) has a maximum thickness of 40 feet on Sylamore 

 Creek in Stone County ; it sometimes replaces the Eureka 

 shale ; often it is entirely wanting. At St. Joe a thin bed (4^^) 

 overlies the shale, and a thicker one (2-4 feet) underlies it.* 



Thus far but few recognizable fossils have been found in this 

 formation. 



Above the Sylamore sandstone and Eureka shale is the chert- 

 bearing limestones (sometimes containing sandstones also) 

 which I have called the Boone chert on account of its wide 

 occurrence and development in Boone County. It is found 

 throughout the entire Paleozoic area of jN'orth Arkansas north 

 of the Boston Mountains, and has a maximum thickness of 

 370 feet. 



The next horizon, named by Prof. F. W. Simonds the 

 '' Wyman sandstone," has a thickness of only 10 feet.f Above 

 it the Fayetteville shale (Simonds), a widespread formation 

 north of the Boston Mountains, has a maximum thickness of 

 300 feet near Batesville. 



J^ext, the Batesville sandstone has a thickness of 200 feet in 

 the western part of the state. The Batesville sandstone lies 

 at the top of the Arkansas equivalent of the Keokuk and 

 Burlington. Then follows what I have called the Boston 

 group, a series of shales, sandstones and limestones, which form 

 the upper portion of the Lower Carboniferous or Mississippian : 

 these taken together have a maximum thickness of 780 feet. 

 This brings the section to the base of the Coal Measures or 

 Pennsylvanian. 



In the Boston Mountain region the lowest member of the 

 Pennsylvanian series, the Millstone Grit, has a thickness, in 

 places, of 500 feet.:!: With the exception of some of the sand- 

 stones and shales that have been extensively eroded in that 

 region, this is the highest member of the series exposed along 

 the north side of the Boston Mountains, and the remainder of 

 the group must therefore be measured in the Arkansas Yalley. 



* In Tennessee, Safford reports a similar sandstone below the shale (Geology of 

 Tenn., p. 330); Meadows and Brown speak of it both above and below (Trans. 

 Am. Inst. M. E., xxi^, 189, 585, 589); Hayes represents it as below (Sixteenth 

 Ann. Rep. U. S. G-. S., pt. iv, pi. vi). 



f Ann. Rep. Geol Surv. of Ark. for 1891, vol. iv; Geology of Benton County, 

 by F. W. Simonds and T. C. Hopkins, p. 27. 



X Ann. Rep. Geol. Surv. of Ark., 1888, vol. iv, p. 137 ; 1890, vol. i, p. 140. 



