SOME EXPERIMENTS IN FOIDING 



507 



A better way to reproduce overfolds was found, though natural 

 conditions do not appear to be so well represented. Single layers 

 consisting of equal proportions of vaseline and parafhn were pre- 

 pared in long thin sheets whose dimensions were approximately 

 22"X5"X2". By compressing these long thin models, overfolds 

 somewhat resembling the structure sections of the Alps were pro- 

 duced (Figs. 13 and 14). These overfolds had their lower limbs very 

 much drawn out. In at least one case the "tete," or head, of the 



Figs. 13 and 14. — Recumbent folds simxilating nappes de recouvrement. These 

 are overfolds whose lower limbs have been drawn out thin. Compare with Hobbs' 

 contention that in overfolds the upper limbs should be thinned. 



fold was curved down toward the undeformed portion beyond the 

 fold (Fig. 15). 



In some ways these folds were very different from the Alpine 

 folds, as they have commonly been interpreted. According to the 

 standard European interpretation the lower folds were formed first, 

 and were covered successively by more overfolds coming from the 

 south, the direction of the active force. But in these experiments 

 the reverse was always true. The overfolds, as a rule, formed first 

 next to the pressure block, and the later ones farther and farther 

 away. This was in general the earlier experience of Willis.^ In no 

 case was an overturned fold pushed completely over the one beyond 

 it. By the time that one had been pushed to the point where the 



' BaUey WUlis, "Mechanics of Appalachian Folding," Thirteenth Ann. Rept., U.S. 

 Geol. Survey, 1891-92, Part II, pp. 211-82. 



