474 STUDIES FOR STUDENTS 
next below it. In the case of abnormal folds (see pp. 330-332 
of my second article) this differential movement is emphasized. 
Consequent upon the differential movement upon the limbs of 
the fold in weak beds where the shearing motion is largely con- 
centrated, the cleavage is locally flatter than in homogeneous 
rocks. Whether the rocks are homogeneous or heterogene- 
ous the rotation is in opposite directions on opposite sides 
of anticlinal arches or synclinal troughs, being outward for an 
anticline and inward tor a syncline; therefore on opposite limbs of 
a fold the cleavage usually dips in opposite directions. Upon oppo- 
site sides of an anticline the cleavage usually diverges downward, 
and on opposite sides of a syncline ut usually converges downward. 
Ordinarily the rotation of shearing will not go far enough to 
bring the cleavage into correspondence with bedding, and its dip 
will be steeper than the dip of the strata; hence, on opposite sides 
of a fold the variation in the dip of cleavage ts less than the variation 
in the aip of bedding. However, in the case of much-compressed 
normal composite folds (Figs. 8 and 11 on pp. 321 and 323) the 
force of gravity and unequal thrust control the direction of the 
moving force, and consequently the form of the secondary folds. 
In this case the cleavage may be rotated from its ordinary posi- 
tion, and upon opposite sides of the anticlinorium the cleavage 
may converge downward and upon opposite sides of the synclin- 
orium may diverge downward. This applies as well to the cen- 
tral fan folds as to the minor folds on the flanks (Fig. 9, on p. 
B21). . 
It has been pointed out (p. 341) in the case of much-inclined 
or overturned folds, that the resultant differential movement or 
shearing between the strata on the steeply inclined or overturned 
limb may be down for a geologically superior stratum as com- 
pared with an inferior stratum. It follows that the shearing on 
both limbs of the fold is in the same direction, and therefore 
that zm regions of overturned monoclinal folds the cleavage may be 
rotated in the same direction throughout, and will hence be monoclinal. 
Since on monoclinal folds the differential movement is great on 
the longer and flatter limb of the fold, the cleavage may be 
