82 
ELEMENTS OF GEOLOGY. 
would be seen by the person on shore to be at an angle of 
40°. If, therefore, our observations are confined to a vertical 
precipice facing in one direction, we must endeavor to find a 
ledge or portion of the plane of one of the beds projecting 
beyond the others, in order to ascertain the true dip. 
If not provided with a clinometer, a most useful instru¬ 
ment, when it is of consequence to determine with precision 
the inclination of the strata, the ob¬ 
server may measure the angle with¬ 
in a few degrees by standing ex¬ 
actly opposite to a clifiT where the 
true dip is exhibited, holding the 
hands immediately before the eyes, 
and placing the fingers of one in 
a perpendicular, and of the other 
in a horizontal position, as in Fig. 
62. It is thus easy to discover 
whether the lines of the inclined 
beds bisect the angle of 90°, form¬ 
ed by the meeting of the hands, so 
as to give an angle of 45°, or whether it would divide the 
space into two equal or unequal portions. You have only to 
change hands to get the line of dip on the upper side of the 
horizontal hand. 
It has been already seen, page 75, in describing the curved 
strata on the east coast of Scotland, in Forfarshire and Ber¬ 
wickshire, that a series of concave and convex bendings are 
occasionally repeated several times. These usually form part 
of a series of parallel waves of strata, which are prolonged 
in the same direction, throughout a considerable extent of 
Fig. 63. 
Section illustrating the structure of the Swiss Jura. 
country. Thus, for example, in the Swiss Jura, that lofty 
chain of mountains has been proved to consist of many par¬ 
allel ridges, witfi intervening longitudinal valleys, as in Fig. 
63, the ridges being formed by curved fossiliferous strata. 
Fig. 62. 
