1897.] ASHLEY — GEOLOGY OF ARKANSAS. 305 



region. In the northern part they usually consist of scattered 

 boulders, all the finer material having been removed. At the 

 northern edge of the area, over which it still exists in an undis- 

 turbed condition, it is comparatively thin. But going southward 

 it gradually increases until, at Centre Point, there is an exposure of 

 seventy-five feet of it in a bluff. Mr. Hill estimates that a mile 

 south of Centre Point it has a thickness of two hundred feet.^ 



The undisturbed gravel deposits occupy an irregular area on the 

 west side of the Ouachita river for a mile or two from the river, and 

 from a mile south of Social Hill to Rockport. They occupy all of 

 6 S., 19 W., except the northwest corner. Passing westward the 

 northern escarpment follows the Chalybeate mountain in an irregu- 

 lar line through 20 west, swinging south in ranges 21 and 22 west, it 

 crosses range 23 west about in the centre of 7 south. It reaches 

 this far north in each range to the west until the West Saline has 

 been crossed, west of which gravel was only noted in spots. 



North of this line gravel was found in nearly every township east 

 of the West Saline river, occupying areas from five or six square 

 miles down to a few acres. 



Generally these consist of scattered boulders of water-worn nova- 

 culite ; some show a little fine material as though they represented 

 fragments of undisturbed deposits. 



All the beds of the creeks which rise among the novaculite 

 ridges contain more or less water-worn novaculite gravel, but in 

 those in the northeast part of the region this gravel sometimes con- 

 stitutes the valley bottom, the creek cutting down through it, and 

 in places exposing a thickness as high as six feet. Prairie Bayou, 

 Big Hill and Valley Fork of Point Cedar creek are examples of 

 this kind. In the centre of a large curve in the Caddo in 5 S., 

 23 W., section 22, northwest quarter, the deposit of gravel reaches 

 a depth of thirty feet. It is not probable that these are original 

 undisturbed deposits, but remains of a subsequent deposit, made 

 when erosion carried the gravel from the higher ground and filled 

 the valleys faster than the streams could carry it off. 



In 5 S., 28 W., section 24, Mr. Purdue found two elliptical knobs 

 or mounds one hundred feet or more long and fifty feet high, which, 

 to all appearances, seemed to be made up entirely of novaculite 

 water-worn gravel. One of them is known as Round mountain. 



Distribution in Other Regions. — Without asserting an exact cor- 



1 Geol. Stirv. of Ar/c, Ann. Rep. for 1888, Vol. ii, p. 40. 



