DEFORMATION OF ROCKS 329 
folds of the next order which compose it, but the secondary folds 
on the primary fold point slightly inward, although the accom- 
modations between the beds compensate in part for this (Figs. 
15 and 16; see p. 331). As the limbs of the synclinorium 
become steeper the secondary folds on the limbs are thrown 
farther and farther toward the axis of the primary trough. If 
unaffected by other forces, when the primary fold becomes steep 
the secondary folds on the limbs become much inclined or over- 
turned. When the limbs of the primary fold become vertical, 
the secondary folds on the limbs become lying or recumbent. 
In all cases, therefore, the axial planes of the secondary folds 
converge upward and diverge downward. But the force of 
gravity enters to further modify the form of the folds. Whena 
fold is inclined, its own weight and that of the superincumbent 
beds tend to push it over still farther. The effectiveness of 
gravity inthis work is doubtless in part due in many cases to par- 
tial escape from thrust because of the relative rise above the 
deep-seated beds largely transmitting the horizontal 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 stillfarther (Fig.11). When the weight of the super- 
incumbent material is great, these folds may be pressed into a 
recumbent position, even when the primary synclinorium is a 
gentle fold. In the synclinoria on the flanks of the Alps, which 
are secondary to the great primary anticlinorium, the crests of 
the recumbent secondary folds sometimes nearly meet, thus 
almost closing the synclinorium. 
The question may be raised as to the effectiveness of super- 
incumbent weight in pressing down inclined folds. It has been 
explained’ that zones of folding of rock masses are necessarily 
zones of readjustment or of partial rock flowage. The flowage is 
from the places of great compression to the places of less compres- 
sion. Wherethe weight of the superincumbent strata is so great 
as to equal or surpass the strength of the rocks folded, it appears 
*This JOURNAL, Vol. IV., pp. 209-212. 
