ROCK FOLDS DUE TO WEATHERING 



MARIUS R. CAMPBELL 



The recent article by Professor Sardeson on "The Folding of 

 Subjacent Strata by Glacial Action"^ is of considerable interest, 

 and doubtless he has a case in which he can demonstrate the origin 

 of the movement; but in studies of this kind it should be borne in 

 mind that folds of a similar character occur far beyond the hmit of 

 glaciation, and that before attributing surface folds in general to 

 glacial action other possible causes should be considered. 



During a recent visit to the Carboniferous coal-field of Arkansas 

 the writer had a good opportunity to examine a number of minor 

 surface folds, which are very common in the great synchnal valleys 

 adjacent to the Arkansas River. In most cases the folds were simply 

 apparent in the disturbed sandy shales or thin-bedded sandstones 

 in the roadway, and it was impossible to determine, without con- 

 siderable excavation, the depth and extent of the disturbance. 



In one case, however, an excellent example was obtained, which 

 is illustrated in the accompanying cut. The occurrence is in the 

 north part of Section 2, T. 7, N., R. 25 W., in the central northern 

 portion of Logan County and about 50 miles east of Fort Smith. 



The locality in which the fold is exposed is a shallow quarry in 

 which sandstone for the construction of the large CathoHc college 

 near Spielersville was obtained. The surface material, as shown 

 by the figure, consists of sandstone, the beds of which range in thick- 

 ness from I to 5 or 6 inches. Near the bottom of the section shown 

 in the cut is a rather heavy bed with a thickness of a foot or 18 

 inches. This is the main rock which is quarried, the surface material 

 simply being stripped off for this purpose. 



As shown in the photograph, the lower beds, especially the thick 

 layer just mentioned and all below it, pass under the fold without 

 being disturbed, the rocks having a dip of about 3° to the south- 

 west. Not only does the heavy bed shown at the bottom of the 



I Journal of Geology, Vol. XIV, No. 3, pp. 226-32. 



718 



