282 A. H. PURDUE 



of these are as low as 15 degrees and they seldom exceed 60 degrees. 

 This means that, at the points of greatest overturning, the rock 

 layers lie literally upside down, and, in folding, have described an arc 

 of 165 degrees. 



The surface rocks about the hot springs are shown in the following 

 section:' 



Feet 



Stanley shale 3,5°° 



Carboniferous 1 tt ^ o • j ^ 



( Hot bpnngs sandstone 100 



j Arkansas novaculite 380 



° I Missouri Mountain slate 50 



. . ( Polk Creek shale 210 



Ordovician. . . i -r,- r ■, ■, , 



[ Bigfork chert 570 



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

 Throughout most 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 is intensely fractured from the folding it has suffered. 



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

 black, somewhat siliceous shale, though soft enough from its graphitic 

 nature to soil the fingers in handling. The upper part contains a few 

 thin, siliceous 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 vicinity 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 formation 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 



1 With the exception of the Stanley shale and the Hot Springs sandstone, these 

 names were first applied to the formations as they appear in Montgomery County, 

 Arkansas. 



2 This name has not been used before in Arkansas. 



