Geology of the Paleozoic area of Arkansas south of the novaculite region / by George H. Ashley.

  • George Hall Ashley
Date:
1897
Catalogue details

Licence: Public Domain Mark

Credit: Geology of the Paleozoic area of Arkansas south of the novaculite region / by George H. Ashley. Source: Wellcome Collection.

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    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-
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