232 FREDERICK W. SARDESON 



filled with residuary clay, and that the lateral compacting of the 

 clay gave the initial upward thrust. The folds had, however, pro- 

 gressed too far for the conditions of their first stages to be discernible. 

 The presence of residuary clay gave them some resemblance to the 

 case of upfolding by frost as described (Fig. i). 



Regarding the general manner of upthrusting, presumably any 

 weakness of rock structure could serve to determine the point where 

 a folding of strata would begin. The other conditions for such 

 folding are first a seam along which the strata might be caused to 

 slide, and then the force necessary for such movement. This force 

 appears to come through a gravel bed from a moving glacier. 



In a former article^ I have described a similar dislodging of 

 stratified rocks, in a way which caused large masses to be rotated 

 up into the glacier, and thus transported without complete loss of 

 stratification. In the cases now described, the tendency is rather 

 toward complete loss of stratification. One may readily imagine 

 from the appearance of the fold (Fig. 2) that in nearly all such cases 

 the disturbing of the strata when once begun, would end only with 

 complete disruption of the loosened mass and an intimate mixture 

 with glacial gravel and till. Many masses occur in the drift of 

 this region which consists largely of crushed stone and shales with 

 the colors and characteristics of the known stratified rock, but with- 

 out the stratification or the fossils preserved in them. 



I Journal of Geology. Vol. XIII (1905), p. 351. 



