Features of the Earth's Surface. 469 
(z.) Fisswres and slips.—The enormous foldings of the strata 
which must occur in the formation of mountain chains by 
lateral thrust would, of necessity, produce fractures at right 
angles to the direction of thrust, or parallel to the folds, 2 e., 
to the range. The walls of such fissures would often slip by 
readjustment by the force of gravity ; or else might be pushed one 
over the other by the sheer force of the horizontal thrust. The first 
case would give rise to those slips in which the foot wall has 
examined the so-called volcanic rocks on this coast, both in 
the Sierras and in the Coast chain, but especially in the former, 
