2 3 8 



DISPLACEMENTS OF STRATA 



the rate of deposition, that almost the entire thickness was accumu- 

 lated in shallow water, as is indicated by the character of the rocks 

 themselves. Geanticlines are less easy to detect, but there is evi- 

 dence to show that they do occur on an equally great scale. 



Fig. q6. — Asymmetrical open fold. High Falls, Ulster County, N.Y. 

 (U.S. G. S.) 



Folds may be classified either in accordance with the relation 

 which their opposite limbs bear to each other, or with reference 

 to the degree of compression to which they have been subjected. 

 Using the first method, we may distinguish the following varieties. 



Upright or Symmetrical. — In this case the two limbs of the fold 

 dip at the same angle, the plane of the axis of the flexure is verti- 



