
128 STRUCTURAL AND FIELD GEOLOGY 
edge on which to place the clinometer—the object being, of 
course, to get as true an average as possible for the whole 
surface. But to insure this, it is always advisable to check 
the result thus obtained by taking the angle of dip at a little 
distance from the section exposed. To do so, the observer, 
standing back from the section, holds the clinometer within 
a short distance of his eye, and in such a position that the 
straight edge of the instrument shall coincide with the lines 
of the dipping strata. The distance at which one should 
make an observation of this kind will depend largely on the 
height of the exposed section. If the height be only a few 
yards the dip may be measured at no greater distance than 
the height. But if the section be much higher the observer 

FIG. I0.—DIP AND STRIKE OF STRATA. 
must stand proportionally further back—the object being to 
make the edge of the clinometer coincide with as long a 
stretch of the lines of bedding as possible. In this way we 
usually get, by means of one observation, a more reliable 
average than we should if we had taken the average of twenty 
observations made by placing the clinometer directly on the 
rock-surface. Even in the case of false-bedded strata, it 
is often possible, by standing well back from the section, to 
get a good average dip for the whole series. But when the 
actual surfaces of the bedding-planes are not visible, the 
beginner may easily be deceived as to the true position of 
the strata. The lines of bedding which are seen travers- 
ing the face of a cliff do not necessarily indicate the true 
direction and amount of dip. Beds that are really inclined 
may even appear to be horizontal. In the accompanying 
