64: H. D. Miser — Llanoria, the Paleozoic Land 



General Geology of the Ouachita Mountains and Arkansas 



Valley. 



The Ouachita Mountains are 50 to 60 miles wide and 

 extend from Little Rock, Ark., to Atoka, Okla., a distance 

 of 200 miles. They are joined on the south and east by 

 the Gulf Coastal Plain. (See figure 1.) The Arkansas 

 Valley just north of the Ouachita Mountains is 30 to 40 

 miles wide and extends westward from near Little Rock, 

 Ark., to near Lehigh, Okla., a distance of about 220 miles. 

 The rocks exposed in these regions are all of sedimentary 

 origin except two small areas of igneous rocks and 

 their related dikes, of Cretaceous age, in Arkansas. They 

 range in age from Cambrian to Pennsylvanian and pre- 

 sent the accompanying composite section. They were 

 formed in a geosyncline to which the name '^Ouachita'' 

 has been appropriately applied by E. 0. Ulrich,^ and they 

 were compressed into numerous nearly east-west folds 

 late in the Pennsylvanian epoch. The maximum thick- 

 nesses of the formations, as given in the section, aggre- 

 gate 37,000 feet, but as the formations vary considerably 

 in thickness from place to place the total thickness in any 

 particular part of these regions would be less than the 

 total just given, though, as pointed out on a later page, it 

 would be great. 



Composite section of exposed rocks of Paleozoic age in the Ouachita Moun- 

 tains and Arkansas Valley. 

 TMcJcness in feet Bemarlcs on occurrence 



Carboniferous : 

 Pennsylvanian 



Boggy shale 2,000a-3,000b 



Savanna sandstone .. .750c-l,o00d Present in Arkansas Valley in Ar- 

 McAlester shale ....1,150^-2,5006 kansas and Oklahoma. 



Hartshorne sandstone. .100fg-300g 



Atoka formation . . .3,000Ji-7,800i Present in Arkansas Valley and 



Ouachita region in Arkansas and 

 Oklahoma. 



Wapanucka limestone ....O^-SOOJ Exposed near boundary between 



Arkansas Valley and Ouachita 

 region in Oklahoma; absent in 

 Arkansas. 



■'Ulrich, E. O., Eevision of the Paleozoic systems, Geol. Soc. America, 

 Bull., vol. 22, pp. 293, 358, 435, -169, 476, 1911. 



a Taff, J. A., U. S. Geol. Survey Geol. Atlas, Coalgate folio (No. 74), col- 

 umnar section sheet, 1901. ^ Taff, J. A., and Adams, G. I., Geology of the 

 eastern Choctaw coal field, Indian Territory: U. S. Geol. Survey Twenty-first 

 Ann. Eept., pt. 2, 278, 1900. c Tafe, J. A., U. S. Geol. Survey Geol. Atlas, 

 Atoka folio (No. 79), columnar section sheet 1, 1902. d Taff, J. A., and 

 Adams, G. I., op. eit., p. 277. e Tafe, J. A., and Adams, G. I., op. cit., p. 



