DEFORMATION OF ROCKS 9)8)0) 
anticlinoria to diverge downward, and for those on synclinoria 
to converge downward. 
Another factor in the production of abnormal composite 
folds is the position of the fold in the group of rocks folded. 
The farther the rocks are below the surface the greater is the 
weight of superincumbent strata and the more forceful is gravity 
in pressing to a recumbent position the inclined secondary and 
tertiary folds of great anticlinoria or synclinoria. As has been 
seen, the inferior strength in the upper strata and the lessened 
weight to which the upper strata are subjected are not usually 
sufficient to prevent thrust and gravity from acting in the ordi- 
nary way and producing normal anticlinoria and synclinoria. 
In both the abnormal anticlinorium and synclinorium the 
application of the above causes to their formation are identical. 
To make this clear the following figures are drawn: Figs. 17 and 
18 each represent four strata, the lower two of which are strong 
and the upper two of which are weak, each figure comprising one- 
fourth of a wave and the other being its complement. In each 
case the figure ends on one side at the crest and on the other at 
the trough of the flexure. There is nothing to indicate whether 
either is a part of an anticline or a syncline. Each, in fact, may 
be half of either, for, put end to end in one way, they form an 
anticline; in the other, a syncline. In both cases the lower 
rocks constitute a relatively rigid inclined plane. If the super- 
incumbent weight is not too great when thrust occurs, in certain 
cases the softer rocks above may yield to the forces to a greater 
degree than do the rigid rocks below, and thus tend to flow over 
them, and in case the upper strata be much weaker than the 
lower, or there be a plane of weakness, the differential flow will 
be largely concentrated along the contact or weak zone, and 
normal secondary folds which have before developed may be 
inclined in an opposite direction from their first position, so as 
to become abnormal. This case is represented by the middle 
parts of Figs. 17 and 18. Put together end to end in one way 
the prominent secondary folds form an abnormal anticlinorium ; 
in the other, an abnormal synclinorium. It will be noted that 
