1897.J ASHLEY — GEOLOGY OF ARKANSAS. 293 



Missouri. At places the top of the ridge is strewn with great mono- 

 liths due to the outcropping of a heavy layer of sandstone. In 7 S., 

 26 W., occur parallel lines of similar monoliths sometimes combin- 

 ing to form a low wall. These were found in the south half of 

 section j6, and north half of section 21, and suggest a similarity 

 of structure or continuity with the overturn exposed on Prairie 

 creek. 



In 7 S., 25 W., the Muddy Fork crosses an overturned anticline 

 in section 20, northeast quarter just west of Muddy Fork post- 

 office. The strike places this upon the same axis as the Muddy 

 Fork fold. 



Prairie Creek Anticline. — In 7 S., 25 W., Prairie creek crosses 

 an overturn in section 28, northeast quarter. This is one of the 

 few cases where an overturn can be traced as it folds over, then 

 under. This anticline is exposed also in section 30 on the Little 

 Missouri river. 



Minor Anticlines. — In 8 S., 25 W., some evidence was found of 

 an anticline crossed by Prairie creek in section 5 near the north sec- 

 tion line, and by the Little Missouri in section 6, northern part. 



In 7 S., 25 W., section 20, west of the centre, Mr. Hopkins de- 

 scribes the nose of a ridge which, at this point, is very suggestive of 

 an overturn with dips to the south. 



In 7 S., 26 W., section 30, a mile north of Nathan, the perpen- 

 dicular dips indicate the presence of an anticline, and Dr. Hay ^ 

 reports finding an anticline west of this on the Muddy Fork, near 

 the Nathan-Muddy Fork road. 



VIII. Theoretical Deductions. 



In this chapter we shall discuss briefly some of the problems pre- 

 sented by the structure described in the preceding chapters. 



Origifial Extent of Folded Strata. — A folded layer of rocks does 

 not cover as much space as the same layer spread out, nor would it 

 be a difficult problem to ascertain the difference, if the folds were 

 completely exposed. When, however, it is remembered that we 

 have only an imperfect section along practically a single line 

 (not even a plane), and in addition to this many of the folds are 

 overturned, or so closely squeezed that their upward or downward 

 extension may be a few hundred feet or several thousand feet, and 



1 Geol. Surv. of Ark., An. Rep. for 1888, VoL ii, p. 284. 



