
CHAPTER IX 
INCLINATION AND CURVATURE OF STRATA 
Dip—Apparent and True. Terminal Curvature. Outcrop influenced by 
Angle of Dip and Form of Ground. Strike. Curvature of Strata— 
Monoclinal Folds, Quaquaversal and Centroclinal Folds, Normal or 
Symmetrical Folds, Unsymmetrical Folds, Inversion, Recumbent 
Folds, Fan-shaped Structure, Contorted Strata, Origin of Folds. 
IN considering the formation of rock-beds, some incidental 
reference was made to the fact that strata, which must 
originally have been horizontally disposed, are now frequently 
inclined, and even flexed, folded, and contorted. These and 
other superinduced structures now fall to be described in 
more or less detail. 
Dip.—The df is the inclination of beds down into the earth, 
and is measured in degrees by the angle between the plane 
of the strata and the plane of the horizon. The instrument 
employed for this purpose is called a clznometer—a graduated 
arc with pendulum. For general use it is convenient to have 
the clinometer combined with a compass—with the latter 
one takes the advection, and with the former the degree or 
amount of dip.* When strata are so exposed that the line of 
greatest inclination can be observed, the direction and 
amount of dip are readily ascertained. If the surface of an 
exposed bed be smooth and even we have only to place the 
clinometer upon it, taking care that the edge of the instrument 
is arranged in the direction of greatest slope (ze. the direction 
in which water would flow if poured upon the surface), and 
that the pendulum is swinging freely. The pendulum points, 
of course, to the degree or amount of dip. If the surface be 
not very smooth, one may lay one’s hammer or walking-stick 
upon the rock in the line of dip, and thus provide a longer 
* See Appendix E. 
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