242 ASHLEY — GEOLOGY OF ARKANSAS. [May 13, 



{b) Igneous Rock. — This is well shown at the same locality as the 

 breccia, and there appears to occupy about the same horizon. It 

 was found at about a score of places west of the Cossatot, these 

 being always, where the structure was known, just at the axes of 

 anticlines ; and, as in many places among the novaculite mountains, 

 it is found very close to the novaculite, it may be safely assumed 

 that it is but a short distance above the novaculite, and may well 

 be taken, as has been suggested, as the dividing line between the 

 Silurian and the Carboniferous.^ 



(f) The Thin Bed of Novaculite and Associated Shales. — Notwith- 

 standing the large number of places at which this bed was met with, 

 it only appears in one of the columnar sections. In the Saline sec- 

 tion it appears not much more than one hundred and fifty feet 

 above the top of the black novaculite and shales. It is usually ex- 

 posed near anticlines; in many cases, exposures are found on 

 each side of the anticline. This would place it low in the series, 

 but the distance between the exposures, frequently a quarter of a 

 mile, and the distance of exposures from the thick-bedded novacu- 

 lite, where exposed in the fold over a novaculite ridge, suggest that 

 generally this thin layer of novaculite is several hundred feet above 

 the black novaculite. Considering the thickness of the bed, from 

 three to ten inches, it is remarkably persistent ; the most southern 

 exposures in township 7 S. appearing practically identical in thick- 

 ness and character with the exposures close to the novaculite ridges. 



In the Saline section it is in a thick bed of sandstone. In a fine 

 exposure on the Caddo in 5 S., 23 W., section 21, northwest corner, 

 there are thick beds of shale above and below it, and it shows this 

 difference in many exposures. 



Whether or not it is above or below the lowest of the beds which, 

 by their fossils, are known to be Carboniferous, is not known. If it 

 is below and belongs to the Silurian novaculites, we must acknowl- 

 edge the existence of belts of Silurian strata all through the area. 

 If it is above, as seems possible, we have the remarkable case of 

 unusual conditions which dominate in one age returning after a 

 long interval in a much later age, not in a single locality, but wide- 

 spread though of short duration. 



(^) The Grit or Fine Conglomerate. — In PI. i. Sec. iv, on the 



1 Geol. Surv. of Ark., An. Rep. for 1890, Vol. i, p. 128, and Vol. ii, p. 375. 

 For doubt regarding the igneous nature of some ot these beds see footnote on 

 p. 232. 



