1S97.] ASHLEY — GEOLOGY OF ARKANSAS. 221 



origin, having been deposited since the close of the Carboniferous 

 age ; the harder rocks on the landward side having been deposited 

 during the Carboniferous and preceding ages. The former, which 

 includes the Mesozoic and Cenozoic, has been termed the Neozoic 

 addition. The line between the two has been traced down the 

 Atlantic coast and through northern Georgia, Alabama and Mis- 

 sissippi, thence following the Tennessee river into southern Illinois, 

 where it turns, crossing the Mississippi near Cairo and running ap- 

 proximately southwest on the west side of the St. Louis, Iron 

 Mountain and Southern Railway nearly to Arkadelphia, where it 

 turns westward and follows an irregular line into the Indian Terri- 

 tory and Texas. 



The region described in the present report lies in a belt just north 

 of that portion of the above line running west from Arkadelphia. 

 To define and locate it more clearly we shall first review the 

 general geologic features of the region from this line to the 

 Arkansas river as shown in the reports already published upon that 

 area.^ 



The history thus revealed is briefly : 



1. A long period of deposition running from early Silurian times 

 through the Carboniferous age, and the accumulation of deposits of 

 great thickness. 



2. These deposits give way to mountain-making forces and becom- 

 ing much folded are lifted into an anticline, called by Dr. Branner the 

 " Ouachita uplift." The axis of this anticline is an approximately 

 east and west line running from Little Rock west well into the 

 Indian Territory. 



3. A period of erosion during which the uplift is cut down until 

 the Silurian strata are exposed along the axis. The later beds are 

 successively exposed as one goes away from the axis of uplift. 



4. A period of depression and deposition upon the southern 

 slope of the Ouachita uplift. During this period, and up to the 

 present time, there has been a series of oscillations of level, result- 

 ing in slight nonconformity between the strata. 



The rocks are now exposed in the following order : 

 I. A belt of Silurian exposures running from Little Rock a little 

 south of west to Dallas, of which the novaculites' are prominent 



1 Geol. Siirv. of Ark., An. Rep. for 1888, Vol. iii; for 1S90, Vols, i and'iii, 



2 Geol. Surv. of Ay-k., An. Rep. for 1890, Vol. iii. 



TEOC. AMER. PHILOS. SOC. XXXTI. 105. P. PRINTED AUGUST 5. 1897. 



