1S97.] DRAKE — THE GEOLOGY OF IXDIAX TEKKITORY. oS i 



south side of the same folds, as is shown in Sees, i, 2, 3, 4, 5, 6, S, 

 and A. This feature is more marked where the folding is inten- 

 sified. Where the anticlines are very closely pressed, overthrows 

 to the north and often faulting along the north side of the anti- 

 clines are the usual consequences; this is shown in Sees. 5, 6 and 

 Pis. II and VII. In the Ozark mountain area the faults are usually 

 normal, while in the Ouachita area the faults are along anticlines. 



All mountains of importance in the southern part of the field 

 (Walker, Black Fork, Rich, Blue, Winding Stair, Jack Fork and 

 Kiamichi mountains) have practically all their beds dipping south 

 about 40°. Throughout the area including these mountains, the 

 folds are so closely pressed, overthrown, and faulted that the strata 

 no longer show broad anticlines with low dips. 



The elevation of the region, the increased intensity of folding 

 toward the south, and the overthrows toward the north all show 

 an upward and northward movement of the rock beds at the time 

 of folding. In places these movements of the strata have pro- 

 duced wrinkles like that shown in Sec. A. 



'^-^ 



-^fe 



Sec. A, To illustrate Ouachita folded structure. Sketched from exposures along 

 a railway cut, five miles southeast of Bengal. 



This movement has tilted beds 40° to the south, the angle at 

 which they best resisted breaking and crushing. As noted by 

 Marcou,^ Branner- and Griswold% these disturbances are probably 

 contemporaneous with the Allegheny mountain uplift, and as noted 

 by Winslow^ they are probably due to the raising of the isogeo- 

 therms in the great thickness of Paleozoic beds. 



Lithology of the Area of the Reconnaissance. — This field includes 

 both igneous and clastic rocks. The igneous rocks, however, are 

 confined to one small granitic dike in the Cherokee Nation. 

 Among the elastics, shales, sandstones, limestones and cherts have 

 extensive developments. 



^Annales des Mines, 5me ser., vii, pp. 339, 340. 

 '-Ann. Rep. Geol. Sur. Ark., 1890, iii, p. 213. 

 '^ Proc. Bost. Soc. Nat. Hist., xxvi, pp. 474-479. 

 ''Bull. Geol. Soc. Am., 1891, ii, pp 231-234, 



