It is thus easy to discover whether the
lines of the inclined beds bisect the angle of 90 degrees, formed by the meeting
of the hands, so as to give an angle of 45 degrees, 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.
(FIGURE 63. Section illustrating the structure of the Swiss Jura.)
It has been already seen, in describing the curved strata on the east coast of
Scotland, in Forfarshire and Berwickshire, 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 country. Thus, for example, in the Swiss
Jura, that lofty chain of mountains has been proved to consist of many parallel
ridges, with intervening longitudinal valleys, as in Figure 63, the ridges being
formed by curved fossiliferous strata, 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.
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