562 



GEOLOGY. 

 Section in Arkansas. 1 



Names of Formations. 



Thickness 

 in Feet. 



Characteristics. 





Potean beds 



3500 



Not described in detail. 





Productive beds 



1800 



Mainly shales and sandstones with some 



II 







coal-beds. 



§§ - 





Barren beds 



18480 







Discontinuity. 







Millstone grit 



500 



Sandstones and conglomerates; friable 







to hard and compact; buff or brown; 







occasionally thin seams of limonite. 







' Kessler limestone 



3-15 



Thin-bedded. 







Coal-bearing shale 



60-90 



Highly fossiliferous; coal seams 6-14 





CO 







inches thick. 





.2 



Pentremital limestone. . 



0-90 



Impure, dark-colored, loose-textured; 











sometimes interbedded with sandstone. 





d • 



Washington sandstone 









o 



and shale 



40-75 



Sandstone and gray shale in varying 

 proportions. 





1 









ffl 



Archimedes limestone . . 



0-80 



Light gray limestone, rich in Archi- 



d 



o3 









medes. 



"p. 





Marshall shale 



0-250 



Black, bituminous shale. 



.& 



Batesville sandstone. . . 



10-200 



Sandstone, sometimes massive cross- 



"co " 



# CQ 







bedded in places. 



"to 



CO 



Spring Creek black shale 







§ 



and limestone 



300 



Black to bluish or yellowish brown in 

 color. 





Wyman sandstone 



0-9 



Sandstone, rather soft. 





Boone chert (including 









St. Joe marble) 



370 



Interbedded strata of chert and lime- 

 stone in varying proportions; contains 

 St. Joe marble, 25-40 feet. 











Sylamore sandstone. . . . 



0-40 



Hard or saccharoidal sandstone and 

 thin-bedded black shale; phosphates. 







Eureka shale 



0-50 







Unconformity. 





Silurian. 







1 The section above the Millstone Grit is for the Arkansas River valley; that below, 

 for the northern part of Arkansas. Adams, 22d Ann. Rept., U. S. Geol. Surv., Pt. II, 

 pp. 83-89; Simonds, Ark. Geol. Surv., Ann. Rept. 1888, Vol. IV, pp. 26-106; Hopkins, 

 ibid. 1890, Vol. IV, pp. 90-94, 253; Penrose, ibid. 1890, Vol. I, pp. 129-139; Williams, 

 ibid. 1892, Vol. V, pp. 273-322; Branner, Am. Jour. Sci., 4th series, Vol. II, 1896 

 p. 235. 



