294 ASHLEY — GEOLOGY OF ARKANSAS. [May 13, 



also that no correlation is obtainable in most cases, it is readily seen 

 that the problem is a difficult one. 



The following method was adopted for obtaining an estimate of 

 the original extent of the folded strata upon the supposition that the 

 folds are not broken, but remain complete until eroded. 



North and south sections on the scale of one mile to the inch 

 were made, as for example, down the Cossatot ; the structure and 

 dips accurately placed on it, and the folds theoretically completed, 

 and then measured with a scale. The folds were made as short 

 as could be done consistently, and the result may therefore be 

 regarded as conservative. Still this method makes no pretense to 

 accuracy, and the limit of error is certainly not more than twenty- 

 five per cent. 



The two best examples gave the following results : The Cossatot 

 section, which is now twenty-four miles long, is estimated to have 

 had an original length of thirty-five miles. The Antoine section, 

 at present twenty miles long, is estimated to have had an original 

 length of thirty-five miles. 



If it be assumed that the movement took place from the south, 

 the strata restored to their original horizontal position would spread 

 over the territory now included in all of Clark, Pike, Howard and 

 Sevier counties and the northern part of Nevada, Hempstead and 

 Little River counties. 



Had such a method been adopted as that used by Prof. Claypole 

 in determining the original extent of a section across Cumberland 

 county. Pa., there is little doubt that instead of thirty-five miles, 

 we should have had between fifty and one hundred miles, as the 

 sections on Antoine creek and Little Missouri river, with their many 

 overturns, present much the same character of structure.^ 



Without going into a full discussion of the subject, we are led 

 to conclude, that while there has been an apparent shortening of 

 north-south cross-sections from their original position of not less 

 than five or ten miles, and possibly much more, did we know the 

 actual facts of the case, it is probable that such shortening has 

 really been very small, and that the strata occupy nearly the same 

 ground as that in which they were laid down. 



Direction of Movement. — In determining the direction of move- 

 ment three factors have been used : the dip of the axial plane 

 of an anticline, or in the case of an overturn, the direction of over- 



1 Claypole, Ajuerican Naturalist, Vol. xix, No. 3, March, 1885. 



