B22 STUDIES FOR STUDENTS 
primary fold diverge upward and converge downward. The 
secondary folds may be ordinary, isoclinal, or fan-shaped. 
The overturned normal anticlinortum.—tThe primary fold of the 
overturned normal anticlinorium has an inclined axial plane, and 
the limbs at corresponding points have equal or unequal average 
dips in the same direction. The primary fold is composed of 
a set of secondary folds, which are overturned in the same 
AN eS 
Ee 
Fic. 10.—Ideal section of an upright normal synclinorium. 
direction as the primary fold. The two sets of secondary axial 
planes on opposite sides of the crest of the major fold diverge 
upward and converge downward. The secondary folds may be 
ordinary, isoclinal, or fan-shaped. 
The upright normal synclinorium.—TVhe primary fold of the 
upright normal synclinorium has a vertical or nearly vertical 
axial plane, and the limbs at corresponding points have nearly 
equal average dips in opposite directions. 
(z) The primary fold is composed of a set of secondary 
folds, each of which is upright, or nearly so, taking the radial 
planes of the primary fold as axial planes of the secondary 
folds. Referring the axial planes to the horizon at the trough 
of the synclinorium, the secondary folds are upright, and in 
passing in either direction transverse to the primary axial planes 
the folds are inclined, but not overturned. The two sets of axial 
planes on opposite sides of the trough of the major fold con- 
verge upward and diverge downward (Fig. 10). 
(0) Inverted intermont trough.t| The primary fold is com- 
posed of a set of secondary folds, which at the center of the trough 
* Les dislocations de Pécorce terrestre, par EMM. DE MARGRIE et ALBERT HEIM 
p. 83. Ziirich, 1888. 
