720 MARIUS R. CAMPBELL 



of this fold, since it lies entirely beyond the southern limit of any 

 known ice-sheet. The movement, however, is just as pronounced 

 as in the cases shown by Professor Sardeson, and it is evident that 

 some competent force other than moving ice has acted in a direction 

 parallel with the bedding in producing the disturbance. 



Since the underlying beds are not affected, it seems evident to 

 the writer that the movement is not due to stresses which affect the 

 crust of the earth to any great depth, for if such stresses are present, 

 the heavy layer shown at the bottom of the photograph and the 

 underlying beds would take the force of the strain, and the upper 

 surface beds would be relieved. Moreover, the folds, so far as they 

 have been observed, are surface features, and in this particular case 

 occur near the outcrop of the beds affected. This entirely precludes 

 the possibihty of the movement being deep-seated, for in that event 

 the rocks lying on the hillside above the fold, and between it and 

 the point of outcrop, would probably have been moved bodily and 

 no fold would have been produced. 



Professor Sardeson has shown that similar features have been 

 produced in Minnesota by the heaving action of frost, but in Arkan- 

 sas the chmate is so mild that freezing could not have played an 

 important part in the formation of a fold. Moreover, the fold is 

 not the result of vertical movement such as described by Professor 

 Sardeson, but movement along the bedding planes of the rock. 



The only way in which freezing could have produced such a 

 result as the fold in question is by the cumulative effect of water 

 freezing in the joints of the rock. This would tend to produce 

 stresses in the surface rocks alone, and these stresses would continue 

 or accumulate until they were relieved by some break or fold in the 

 surface beds. Thus freezing might account for the phenomenon. 

 If freezing alone were the active force, we should, however, find 

 the results of its action much more common in northern regions 

 than in southern; but, so far as the writer is aware, this is not the 

 case. Therefore we must conclude that freezing, while possibly a 

 factor in the case, has not been the dominant one. 



The creep of surface rocks down the slope may be appealed to 

 as a possible cause. It is true that in this region there is a close cor- 

 respondence between the attitude of the beds and surface topog- 



