320 STUDIES FOR STUDENTS 
synclinorium, like a simple fold, may be upright, inclined, or 
overturned, but it is probable that in composite folds of the first 
order of magnitude the last rarely if ever occurs. 
Taking as axial planes the radial planes of the primary fold, 
the secondary folds may be upright, inclined, or overturned, 
or on different parts of the same primary fold each form may occur. 
The radial positions of the axial planes give the proper basis in 
comparing the dynamic processes and effects of folding, but 
Fic. 7.—Ideal section of an upright normal anticlinorium. 
because we rarely see the whole of a great anticlinorium or syn- 
clinorium at a single view, it is perhaps best to treat both the 
primary and secondary folds in reference to the plane of horizon. 
Some of the special cases of composite folds are as follows: 
NORMAL COMPOSITE FOLDS. 
The upright normal anticlinorium.—The primary fold of the 
upright normal anticlinorium 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. Refer- 
ring the axial planes to the horizon, at the crest of the anticline 
the secondary folds are upright, and in passing in either direction 
transverse to the primary axial plane the secondary folds are 
inclined, but not overturned. The two sets of secondary axial 
planes on opposite sides of the crest of the primary fold diverge 
upward and converge downward (Fig. 7). 
