234 J. C. Branner — Paleozoic Sediments in Arkansas. 



removed by erosion. If one turns nearly due east, from the 

 Bayou Meto anticline, crosses the Little Rock and Fort Smith 

 railway a mile or two south of Preston, and goes to the top of 

 Round Mountain in 4 JN^. 14 W. (C on the map), he will cross 

 over the same series of rocks, plus the beds forming Round 

 Mountain. All the way the dip is toward the west, and the 

 total thickness of the exposed rocks is 18,480 feet. 



Another series of observations made along a line run north 

 from the top of Round Mountain to the axis of an anticline 

 three miles north of Conway (D on the map), and deducting 

 for the gentle fold near Conway, gives a thickness of 17,730 

 feet. 



I lay particular stress upon these three measurements because 

 they involve the greater part of the thickness of the Lower 

 Coal Measures rocks, and because, judging from'the manner in 

 which these three sections agree, there seems to be no possibil- 

 ity of any serious mistake in estimating their thickness. 



It ought to be noted here that in 1889 I authorized Mr. 

 Griswold to say that the rocks of the Coal Measures in Arkan- 

 sas had a total thickness of four miles.* This statement was 

 based upon a section examined and measured between the 

 Petit Jean Mountain and the Silurian novaculites of the 

 Ouachita uplift. But there was no certainty that the rocks 

 along this section were not repeated by folds or faults, and the 

 thickness seemed so unusual that I afterwards sent assistant 

 J. F. Newsom (now Professor of Geology in the University of 

 Indiana) over another part of the same beds with a view to 

 checking my results. The three measurements here given 

 from the Cato syncline to the Bayou Meto anticline, thence to 

 Round Mountain, and from Round Mountain to the Cadron 

 anticline, are the results of Professor Newsom's work.f 



So far as I can make out, the sandstones in the top of Round 

 Mountain are at the same geological horizon as those in the 

 tops of Carrion Crow Mountain, Petit Jean Mountain and 

 Mount I^ebo, and these sandstones lie only a short distance 

 below the Ouita coal bed near Russellville. 



From the base of the productive Coal Measures (beginning 

 at the top of Carrion Crow Mountain) to the top of the Poteau 

 Mountain at the Indian Territory line, there is a maximum 

 thickness of 5300 feet, of which 3500 feet belong to the upper 

 series, which Mr. Winslow proposes to call the Poteau group. 



"~* Ann. Rep. Geol. Sur. for 1890, vol. iii, Whetstones and the Novaculites of 

 Ark.; by L. S. Griswold, p. 206. 



f In his report to me Professor Newsom notes the fact that the measurement 

 on the south side of Bayou Meto anticline gives a thickness of 14,900 feet, and 

 that the measurement on the west side, or down its nose to the ridge correspond- 

 ing to that at the synclinal trough on the south, gives 14,520 feet— a difference of 

 only 380 feet. 



