Carboniferous— 
Sia yesh e. menren or, Sion ky shock 5. Sroka hor, 3,900 feet. 
Hot Oprings sandstone. --,\. ah ae noses 323 fton ae 100) >< 
Age unknown— 
AT CANSASBNOVACU TUG Hert tity eas See Se bs Seedy 3880 ‘5 
Missouri vMiountain slate: aus. eee eee oe bom 
Ordovician— 
POTEACTCEKIS NG] Ot eee or ee ae et ae tte Z1Oe ss 
Pom UOUAEHEED (ce Ness 52 Seis eee Teo, BLA || a 
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 noyaculite 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* 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 
+ This name has not been used before in Arkansas. 
