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A. WINSLOW — GEOLOGY OF WESTERN ARKANSAS. 



and this means gradual relief from pressure of the underlying rocks; hence 

 a constantly diminishing load opposes the forces tending to cause protrusion 

 of the lower layers. Thus it is conceivable that expansion or protrusion 

 may take place coincidently in a general way with the removal of the load. 

 An immediate effect of such protrusion would be to increase the dip of the 

 rocks adjacent to it, as is illustrated by figures 7, 8 aud 9, which are ideal 

 sections across such an arch. They show the successive changes of dip with 

 the progress of degradation. The effect of such an interpretation of the 

 origin of dips upon the represented length of a flexed stratum will be at 



Figure 7. — Ideal Section of Arching Strata. First Stage. 



Figure 8 — Ideal Section of Ai ching Strata. Second Stage. 



Figure 9.— Ideal Section of Arching Strata. Third Stage. 

 Ideal sections illustrating the progressive increase of dips with progressing degradation. 



once appreciated. In ffgures 7, 8 and 9 the relative lengths of the lines 

 connecting the points A and B are respectively 23, 25 and 30. May not 

 the apparently excessive estimates of linear compression in many instances 

 have been due to such a cause ? 



The Physiographic Geology. 



The general Surface. — The surface features of western Arkansas are typ- 

 ically those of stratified non-metamorphosed rocks, and their mode of pro- 

 duction has been such as usually characterizes such rocks. The stage of 

 topographic development here may be classed as mature, in that it includes 



