S97.1 ASHLEY — GEOLOGY OF AKKANSAS. 253 



where distinct anticlinal ridges with synclinal valleys between were 

 found. 



The Cossatot Section. — Fig. 2, Plate II, gives a section up the 

 Cossatot river to the mouth of Brushy Fork, and thence up Brushy 

 Fork to the north line of 4 S. The dip is north with many over- 

 throws to the south. The southern end is not as closely folded as 

 would be the case further east. The presence of one or more lay- 

 ers of shale or shaly sandstone has assisted materially in determining 

 the structure. The exposures along the Cossatot are more numer- 

 ous and the structure ascertainable with more certainty than on the 

 Antoine. The novaculite is not exposed except at the extreme 

 northern end of the section ; but at many places it cannot be far 

 from the surface, as it comes to the surface but a short distance east 

 in Rachel and Raspberry mountains, and a short distance west in 

 Cross mountain. 



Directio7i and Genei'al Character of the Folds. 



Eastern Sheet. — The structure of the eastern portion of the Lower 

 Coal Measures area is obscure, and, as the map shows, but little 

 understood. 



This is due to three causes. Principally the prevalence of over- 

 turns ; next, the fact that erosion has progressed until the streams 

 are comparatively slow, with banks neither high nor precipitous, 

 thus presenting few fresh exposures of rock ; and again, the wide 

 distribution of water-worn material which conceals everything. 



From these causes the number of exposures found giving a dip 

 and strike would average less than one to the square mile ; in many 

 townships they are as low as one in four to eight square miles. If a 

 complete structural map of the region could be made it would prob- 

 ably show many more folds than are here indicated. At the eastern 

 end of the map the anticlines and synclines all run nearly due 

 west. In range 21 W. they all bend south, running 12° to 15° 

 south of west. The Suck creek anticline and Bell's creek anticline 

 are exceptions to this rule. 



West of range 23 the folds in township 4 S. regain their due 

 west course, the folds to the south maintaining the direction of 12° 

 to 15° south of west. Of the anticlines shown, about one-half are 

 overturns. Indications suggesting the existence of many other 

 overturns were found, but they were not well enough marked to 

 warrant their insertion. 



PROC. AMER. PHILOS. SOC. XXXVI. 155, R. PRINTED AUGUST 6, 1897. 



