480 SLODLES AOL SURG EIN AES: 
The above phenomena (probably secondary to cleavage) are 
finely illustrated in the quartzites of the North Range of Bara- 
boo, Wisconsin and in the massive graywackes of the Ocoee 
series on the Hiwassee_ River, Tennessee, combined with cross 
and parallel secondary structures, as shown by Fig. 10. It is 
possible that in the cases of both cleavage and fissility as the 
folding becomes closer and closer the zones of much shearing 
may extend farther and farther into the rigid beds, producing 
secondary structures nearly parallel to bedding throughout the 
limbs of the folds. If the thrust be so powerful as to give the 
layers isoclinal dips, the secondary structures and bedding will 
be developed or rotated so as to be nearly parallel throughout 
the rock-mass, except at the sharp turns on the crests of the anti- 
clines and in the troughs of the synclines, just as in the case of 
normal plastic flow in homogeneous rocks. (See pp. 464-465). 
RELATIONS OF CLEAVAGE AND FISSILITY TO EACH OTHER. 
GRADATION BETWEEN CLEAVAGE AND FISSILITY. 
In passing downward from the zone of fracture to the zone 
of flowage, one would naturally expect to find all gradations 
between fissility in two directions developed in the maximum 
shearing planes and cleavage in a single direction developed in 
the normal planes. To this natural expectation the phenomena 
seem to correspond. Rocks are found having two planes of 
fissility intersecting nearly at 90° ; others which intersect each 
other somewhat more acutely, so that the rock breaks up into 
forms having rhombic or rhomboidal sections ; others in which 
the rhombs or rhomboids have their axes very long in one direc- 
tion as compared with those in the other ; and others in which 
the two directions are so nearly parallel that they are not sepa- 
rated, except by close observation. 
According to Beckert and Hoskins,? somewhat inclined inter- 
‘Finite Homogeneous Strain, Flow, and Rupture of Rocks, by GEORGE F. 
BECKER, Bull. Geol. Soc. Am., Vol. IV, 1893, p. 50. 
?Flow and Fracture of Rocks as related to Structure, L. M. Hoskins, Appendix 
to Principles of North American pre-Cambrian Geology, by C. R. VAN HIsE, Sixteenth 
Ann. Rept. U.S. Geol. Surv., for 1895-6, pp. 872-874. 
