70 H. D. Miser — Llanoria, the Paleozoic Land 



the iiorth border of the Ouachita region near McAlester, 

 Okla.,^^ and also in the Ozark region, though in that region 

 they may be represented by comparatively thin lime- 

 stones, sandstones, and shales of Mississippian age. 

 It may be suggested that these two formations for- 

 merly extended much farther west and north and 

 that their absence is due to erosion, but there is no 

 evidence to indicate that any considerable thickness 

 of strata was removed by erosion from the Arbuckle 

 and Ozark regions during the Mississippian epoch. 

 Not only do the formations themselves become thinner 

 toward the north, but sandstone beds that form about 

 one-fourth of the Stanley shale along the southern 

 border of the Ouachita region become thinner or thin 

 out completely before they reach the north side of 

 the region, and the Jackfork sandstone changes 

 toward the north from a formation composed almost 

 entirely of sandstone with very little shale to a for- 

 mation composed largely of shale. This northward 

 thinning of the sandstone beds of the Stanley shale 

 and the dovetailing of thick beds of shale in the 

 Jackfork sandstone to the north imply a southern 

 source for the sand and mud that later formed these 

 formations. Many small quartz pebbles, one-fourth of 

 an inch or less in diameter, occur in the Jackfork sand- 

 stone, particularly in its lower part, on the southern 

 border of the Ouachita Mountains. They become less 

 abundant toward the north. The enormous thickness and 

 comparatively large areal extent of the Stanley and 

 Jackfork indicate that the land mass to the south suffered 

 great erosion. From the evidence now at hand the 

 Ai^buckle and Ozark regions could not have supplied so 

 vast a quantity of sediment during the Mississippian 

 epoch. 



The northward thinning of the sandstones in the forma- 

 tion to which the name Stanley shale is applied was noted 

 by L. S. Griswold,^^ who says, ^' The existence of sand- 

 stone beds overlying the novaculites on the south side of 



^3 Girty, G. H., The fauna of the Caney shale of Oklahoma, U. S. Geol. 

 Survey, Bull. 377, p. 6, 1909. Wallis, B. T., The geology and economic value 

 of the Wapanucka limestone of Oklahoma, Oklahoma Geol. Survey, Bull. 23, 

 p. 27, 1915. 



" Griswold, L. S., Whetstones and the novaculites of Arkansas, Arkansas 

 Geol. Survey, Ann. Kept, for 1890, vol. 3, pp. 193, 213, 1892. 



