1897.1 ASHLEY — GEOLOGY OF ARKANSAS. " 233 



sibly related to the sandstone is a white, friable, decomposed sand- 

 stone found at a few places. A typical locality is in fields about a 

 mile north of Amity near the Caddo Gap road. It crumbles be- 

 tween the fingers into a white, dust-like powder ; when dry it is 

 almost as white as chalk. This soft, decomposed condition ex- 

 tends to such a depth that gullies once started in it, cut deep, 

 canon-like ditches resembling those so common in the soft Creta- 

 ceoul marls of the region to the south. 



In this sand are great numbers of concretionary ironstones, from 

 the size of the fist up to three or four feet in diameter. These are 

 strewn over the surface, or protrude from banks, or occasionally 

 may be observed capping a short column of the surrounding soft 

 material. They are usually dark brown and consist of several 

 layers averaging half an inch thick in which the proportion of iron 

 is quite large, surrounding a kernel of exceedingly tough gray 

 sandstone. 



Beside the ironstones, this sand is found in some places inter- 

 sected by numerous joint-planes filled with thin films of iron. 

 Quartz veins and crystals are especially abundant in localities of 

 this nature. Through the sand are frequently little nodules of 

 silicious shale invariably incrusted with a soft, yellow layer. These 

 iron incrustations are formed by waters dissolving out the iron and 

 other impurities which are again deposited in the numerous joint 

 planes ; the quartz is deposited at the same time. Quartz filling 

 the crevices in the sandstone is abundant over most of the area. 

 While in some places this forms only a film just thick enough to give 

 a sparkling appearance to the rock when broken open, in others 

 it occurs as solid veins a foot or more in thickness, which may 

 withstand weathering better than the enclosing rocks and may 

 appear as a low wall across the country. The smaller veins, as a 

 rule, intersect the bedding planes at right angles or at a high angle ; 

 but many of the larger ones run parallel to the strike. There is 

 such a case in 7 S., 32 W., sections 8 and 9, on Robinson's Fork 

 of the Rolling Fork of Little river, where a protruding vein of 

 quartz can be traced a mile or more in the line of strike. 



Masses of interlocking crystals occur frequently, and occasionally 

 well-formed single crystals are found. In many places in the 

 western part of the region, the ground is completely covered with 

 fragments of quartz, as on the ''line road " in 5 S., 32 W., section 

 25, where the road is paved with quartz for nearly half a mile. 



