1897.] 



ASHLEY — GEOLOGY OF ARKANSAS. 



259 



yet, when it is considered that, on account of the density of the 

 forest, it is but rarely that the '* lay of the land " can be made out 

 for more than one or two hundred yards from the course pursued, 

 it will be understood why, in a rapid reconnaissance like that un- 

 dertaken, but little more than suggestions could be obtained from 

 the topography. For these reasons the structure has, in no case, 

 been assumed from the topography alone. 



Overturns. — Overturns are a common feature of the area. In 

 Fig. 13 is a simple overturn, and on the right side (Fig. 14) are 

 shown the corresponding dips of beds at surfaces of different levels 

 as AB, CD, EF, GH. Thus, in the case of A'B' the axis is readily 

 recognized ; but remembering that no correlation of beds can be 

 made, the section at that point would naturally be interpreted as an 



^ -^ 



B' 



1^ '^^ ^S. D 



'^^i ^ ^ "^rt' 



Figs. 13, 14.- 



-Diagrams illustrating the structures shown by eroding an 

 overturn to different depths. 



anticline at b and a syncline at a. Such overturns are liable to 

 lead to a confusion which can only be cleared up by careful detailed 

 work. 



In CD' and E'F', the structure is the same, but is somewhat 

 modified. 



Most of the overturns found have been eroded so as to give ex- 

 posures between those of CD' and E'F'. Sometimes there is a 

 marked change in the dip on the two sides, as a low north dip on 

 the upper side and a high north dip in the underfolded strata. 



In such a case an overturn is suggested, and if an exposure giving 

 a dip contrary to the general dip can be found, as c in CD', it has 

 generally been considered as confirming the probable existence of 

 an overturn at that point. 



In many cases the only actual evidence obtainable is a single dip 

 or two contrary to the general direction of dip. In such a case. 



