271 



Carboniferous — 



Stanley shale 3,500 feet. 



Hot Springs sandstone 100 " 



Age unknown — 



Arkansas novaculite 380 " 



Missouri Mountain slate 50 " 



Ordovician — 



Polk Creek shale 210 " 



Bigfork chert 570 " 



The Bigfork chert is in layers from two to twelve inches thick. 

 Throughout a good portion of the formation it consists almost entirely of 

 chert, but in parts the layers are separated by thin beds of shale, and in 

 other parts shale is the main constituent. The chert is very brittle and 

 intensely fractured from the folding it has suffered. 



The Polk Creek shale overlies the Bigfork chert, and is a very black, 

 somewhat silicious shale, though soft enough from its graphitic nature to 

 soil the fingers in handling. The upper part contains a few thin silicious 

 beds, but the lower part is wholly shale. 



The Missouri Mountain slate as it occurs in the vicinity of the hot 

 springs is a red to brown or yellow shale, depending upon the stage of 

 weathering. Further west in the Ouachita area it is a true slate. 



The Arkansas novaculite as it is exposed in the city of the hot springs 

 consists of three parts : A lower, massive one 275 feet thick, made up of 

 heavy beds of much fractured novaculite. It is from this part of the for- 

 mation that the Arkansas abrasives are secured. This is followed by 

 fifty-five feet of very black clay shale, weathering in places to light gray; 

 and this by fifty feet of what appears to be rotten, porous novaculite. 

 The section of the novaculite formation over the Ouachita area varies 

 greatly with the locality. 



The Hot Springs sandstone 4 is a gray, quartzitic sandstone in beds 

 from three to eight feet thick. The basal ten feet or more is conglomeratic. 

 It is from this formation that most of the hot springs issue, which fact, 

 however, is accidental and consequently not significant. 



The Stanley shale is composed mainly of black to green clay shale, 

 though a large per cent of it consists of rather soft, greenish sandstone. 

 This shale skirts Hot Springs and West Mountains. While a large part 



4 This name has not been used before in Arkansas. 



