DIP AND STRIKE. 
81 
degrees. The strike^ or line of hearing^ is the prolongation 
or extension of the strata in a direction at right angles to 
the dip; and hence it is sometimes called the direction of 
the strata. Thus, in the above instance of strata dipping 
to the north, their strike must necessarily be east and west. 
We have borrowed the word from the German geologists, 
streichen signifying to extend, to have a certain direction. 
Dip and strike may be aptly illustrated by a row of houses 
running east and west, the long ridge of the roof represent¬ 
ing the strike of the stratum of slates, which dip on one side 
to the north, and on the- other to the south. 
A stratum which is horizontal, or quite level in all direc¬ 
tions, has neither dip nor strike. 
It is always important for the geologist, who is endeavor¬ 
ing to comprehend the structure of a country, to learn how 
the beds dip in every part of the district; but it requires 
some practice to avoid being occasionally deceived, both as 
to the point of dip and the amount of it. 
If the upper surface of a hard stony stratum be uncovered, 
whether artificially in a quarry, or by the waves at the foot 
of a clilf, it is easy to determine towards what point of the 
compass the slope is steepest, or in what direction water 
would flow if poured upon it. This is the true dip. But 
the edges of highly inclined strata may give rise to perfectly 
horizontal lines in "the face of a vertical cliff, if the observer 
see the strata in the line of their strike, the dip being inward 
from the face of the cliff. If, however, we come to a break 
in the cliff, which exhibits a section exactly at right angles 
to the line of the strike, we are then able to ascertain the 
Fig. 61. 
Apparent horizontality of inclined strata. 
true dip. In the annexed drawing (Fig. 61), we may sup¬ 
pose a headland, one side of which faces to the north, where 
the beds would appear perfectly horizontal to a person in the 
boat; while in the other side facing the west, the true dip 
