296 ASHLEY — GEOLOGY OF ARKANSAS. [May 13, 



subjected to horizontal pressure, evenly applied, will not tend to 

 bend, but to be compressed, as in Fig. 33<^. If, however, as in Figs. 

 34« and 35^, it have a slight initial dip, the horizontal force will, at 

 the point or points of bending, be resolved into two components, one 

 tending to compress and the other to bend. Bending may then 

 take place, but all that is desirable to note here is that, if the bend- 

 ing is carried to overturning, the direction of overthrow is not 

 determined by the direction of movement, but by the direction of 

 dip, as suggested in Figs. 34^ and 35^.^ 



It is true that as a rule this dip will be toward the open sea, and 

 the testimony of other elements show that, in many cases at least, 

 the movement or apparent movement has been from the shore sea- 

 ward. In such a case the overthrow will be away from the shore, 

 and so there would be a tendency for the rule to hold good that 

 the overthrow is away from the direction of movement. But we 

 are led by the facts observed in this area where there exist over- 

 throws both to the north and south to believe that such reasoning 

 from the direction of overthrow is reasoning in a circle and not to 

 be accepted as trustworthy. 



Another element is the direction of dip of faults. This, too, con- 

 tains the same objection, for, as shown by Daubree,'^ faulting parallel 

 to the strike is governed by the folding, and if, as we are led to 

 suspect, the folding is not entirely governed by the direction of 

 movement, we must consider the faulting as under the same limita- 

 tions and therefore not a trustworthy factor. 



If a section across the Appalachians from southeast to northwest 

 be examined, it will be noticed that the folding, which is intense 

 at the southeast end, gradually becomes more and more gentle un- 

 til at the northwest end the strata become horizontal.' An ex- 

 amination of Fig. I, shows the same thing ; in this case the intensity 

 dies out from south to north. In such cases the evidence seems to 

 be strong, that movement, if any, comes from the direction of 

 greatest or closest folding. This suggests that the movement in 

 our region was from the south. 



1 Dr. E. A. Smith has suggested the same explanation for overthrust and under- 

 thrust (^Am. Jour. Set., April, 1893, P- S^^), but as Mr. Ashley's paper was 

 written before the publication of that paper his explanation is allowed to stand. 

 — J. C. Branner. 



2 Daubree, Geologie Expervnentale, Paris, 1879, p. 344. 



3 H. D. Rogers, First Geological Survey of Pemisylvai^ia, 1S57. 



