246 ASHLEY — GEOLOGY OF ARKANSAS. [May 13, 



mountains gradually dip south and disappear under the heavy beds 

 of the Coal Measures which fill the syncline of the Arkansas river 

 basin. If these beds persist to the south they should appear again 

 on the north side of the Ouachita uplift, and should disappear with 

 a south dip on the south side of the uplift. The State Geologist 

 is of the opinion that the grits described in this area represent the 

 southern extension of the Millstone Grit of north Arkansas. The 

 two are identical in appearance, except that the rocks of the south- 

 ern area are never as coarse grained as some of that to the north. 



The Millstone Grits of north Arkansas are at the bottom of the 

 Coal Measures; so that if the grits south of the Ouachita uplift be 

 correlated with those of north Arkansas we must consider that we 

 have strata referable to both the Coal Measures and Lower Carbon- 

 iferous or Mississippian series. 



Without regard to time, it seems highly probable that the strata 

 south of the Ouachita uplift were originally continuous with those 

 just north of it. No direct proof of this has been found, nor has 

 anything been found that conflicts with this theory. 



Previous Correlations, 



Thomas Nuttall, who was in this part of Arkansas in 1819, pub- 

 lished many observations on the geology, but he found no fossils in 

 these lower sandstones and made no attempt to correlate them.^ 



In 1834, G. W. Featherstonhaugh, U. S. Geologist, made an 

 examination of the elevated country between the Missouri and Red 

 rivers." 



He passed along the eastern edge of our region and down the 

 Ouachita river. The ferruginous sandstones he referred to the Old 

 Red Sandstone (Devonian) of England, which he thought to rest 

 upon the grauwacke, the grauwacke being the shales and shaly sand- 

 stones at the bottom of the series. 



He failed to recognize the intimate relation between the shale and 

 sandstone or the folded condition of the strata. He was originally 



1 " Observations on the Geological Structure of the Valley of the Mississippi," 

 by Thomas Nuttall, Jour. Acad. Nat. Sci. of Philadelphia, Vol. ii, Pt. i. Phila., 

 1821, pp. 48-52. 



■■2 Geological Report on an Examination fnade in ISoJ/, of the Elevated Coun- 

 try between the Missouri and Red Rivers, by G. W. Featherstonhaugh, Wash- 

 ington, 1835, P- 71- 



