328 SLGIDIGES SHON SIMYIQBIN IS 
the different parts of each anticline and syncline. The large 
basins of deposition are not simple, but undulating. These 
secondary undulations are composed of smaller ones, and so on 
until ripple-marks are reached, and even these are composite. 
Each curve is composed of rhythmical curves of a higher order; 
hence the arch or trough which forms is not simple, but is com- 
posed of a number of minor folds, and these again of those of a 
higher order. 
At first the anticlinorium is upright, or nearly so, as are also 
the folds of a higher order which compose it, but the secondary 
folds on the flanks of the primary fold point slightly outward, 
although the accommodations between the beds compensate in 
part for this (Figs. 15 and 16). As the limbs of the anticlinorium 
become steeper the secondary folds on the limbs are thrown 
farther and farther away from the axis of the primary arch (Fig. 
7). If unaffected by other forces, when the primary fold 
becomes steep the secondary folds on thelimbs become much 
inclined or overturned. When the limbs of the primary folds 
become vertical, the secondary folds on the limbs become lying 
or recumbent. In all cases, therefore, the axial planes of the 
secondary folds diverge upward and converge downward. The 
force of gravity may enter to further modify the forms of the 
folds. When a fold is inclined, its own weight and that of the 
superincumbent beds tend to push it over still farther. The 
effectiveness of gravity in this work is doubtless in part due in 
many cases to partial escape from thrust because of the relative 
rise above the deep-seated beds largely transmitting the hori- 
zontal force. (See p. 318). The farther the secondary folds are 
inclined, either by the increased steepness of the primary fold or 
by the effects of superincumbent weight, the more effective is 
gravity in pressing them down still farther (Fig. 8). When the 
weight of the superincumbent material is great, these folds may 
be pressed into a recumbent position, even where the primary 
anticlinorium isa gentle fold. Thusare explained the composite 
normal anticlinoria of the Alps. 
At first a synclinorium is upright, or nearly so, as are also the 
