432 W. J. MILLER 



Fig. 2 being separated from C by an intermediate mass B of slightly 

 less rigidity would slide over C and cause the portion B to become 

 ruffled or folded. Occasionally parts of zone B would become 

 fractured or faulted. The portion B would need to be only slightly 

 less rigid than the adjacent portions. The somewhat thinner lime- 

 stone layers separated by thicker shale partings would be sufficient to 

 cause the part B to be thus less rigid. A similar explanation would 

 also apply to the lower folded zone. The folded zones thus merely 

 indicate horizons of weakness along which the differential movement 

 has taken place. 



As thus explained it is evident why the strike of the minor folds, 

 the strike of the fault, and the strike of the large low folds of the region 

 should all be parallel, since all these phenomena were produced by the 

 same pressure. Also the local character of the phenomena under 

 discussion is readily explained, since the conditions for their formation 

 exist only in the vicinity of the fault. 



Where phenomena of this kind occur even in regions of low folds, 

 but without faults, it is thought that the above explanation will suffice, 

 because during the process of folding there would be more or less of a 

 tendency for certain strata to slide over others. Where the conditions 

 of relative rigidity, etc., were favorable, certain strata just beneath 

 the sliding masses might become ruffled or folded. 



The locally folded clay layers between non-folded layers along 

 Bla,ck River, above mentioned, are to be explained in a somewhat 

 similar manner. Vanuxem says: "The layers show a series of con- 

 tortions of different kinds, for which no cause can reasonably be 

 assigned but different degress of lateral pressure. " Since there is no 

 noticeable difference between the characters of the disturbed and the 

 undisturbed beds and since the intensity of the folding is often so 

 great, Vanuxem' s explanation is not at all satisfactory. The required 

 differences in degree of lateral pressure are altogether too great. The 

 writer believes that, in principle, the explanation given for the Trenton 

 Falls occurrences applies here also, although in the case of the clay 

 beds the movement of the upper over the lower masses may have 

 been caused by ice action or by having been pulled down the hill- 

 sides by gravity. Or as Salisbury and Atwood'' have suggested for such 



I Jour. Geol., Vol. V, 1897, p. 143. 



