OUTCROP OF STRATA. 
83 
Fig. 64. 
Fig. 65. 
• .*. * a\ 
. -—■ 
n 
c 
7-i; . 
--Y- / -^ 
of which the nature and dip are occasionally displayed in 
deep transverse gorges, called “cluses,” caused by fractures 
at right angles to the direction of the chain.* 'Now let us 
suppose these ridges and parallel valleys to run north and 
south, we should then say that the strike of the beds is north 
and south, and the dip east and west. Lines drawn along 
the summits of the ridges. A, B, would be anticlinal lines, 
and one following the bottom of the adjoining valleys a syn¬ 
clinal line. 
Outcrop of Strata. —It will be observed that some of these 
ridges. A, B, are unbroken on the summit, whereas one of 
them, C, has been fractured along the line of strike, and a 
portion of it carried away by denudation, so that the ridges 
of the beds in the formations a, c come out to the day, or, 
as the miners say, crop 
out^ on the sides of a val¬ 
ley. The ground-plan of 
such a denuded ridge as 
C, as given in a geological 
map, may be expressed by 
the diagram. Fig. 64, and 
the cross-section of the 
same by Fig. 65. The line 
D E, Fig. 64, is the anti¬ 
clinal line, on each side of which the dip is in opposite direc¬ 
tions, as expressed by the arrows. The emergence of strata 
at the surface is called by miners their outcrop^ or basset. 
If, instead of being folded into parallel ridges, the beds 
form a boss or dome-shaped protuberance, and if we suppose 
the summit of the dome carried off, the ground-plan would 
exhibit the edges of the strata forming a succession of cir¬ 
cles, or ellipses, round a common centre. These circles are 
the lines of strike, and the dip being always at right angles 
is inclined in the course of the circuit to every point of the 
compass, constituting what is termed a qua-quaversal dip— 
that is, turning every way. 
There are endless variations in the figures described by 
the basset-edges of the strata, according to the different in¬ 
clination of the beds, and the mode in which they happen to 
have been denuded. One of the simplest rules, with which ev¬ 
ery geologist should be acquainted, relates to the V-like form 
of the beds as they crop out in an ordinary valley. First, 
if the strata be horizontal, the V-like form will be also on a 
level, and the newest strata will appear at the greatest heights. 
* Thurmann, “Essai sur les Soulevemens Ju-rassiques dii Porrentruy." 
Paris, 1832. 
Ground-plan of the denuded ridge 0, Fig. 63. 
