104 



edge is parallel to the horizontal plane, it is ob- 

 vious that such an edge will have a linear direc- 

 tion on some line of the compass, which is at right 

 angles to the inclination, or dip, and indicates the 

 position of the plane towards the meridian. In 

 similar strata, although the edge is not thus pa- 

 rallel to the horizon, the position of the plane 

 with respect to the meridian may be ascertained 

 by a spectator placed in the same line, but the 

 edge will no longer be at right angles to the 

 vertical. 



This position of the plane of a stratum with 

 respect to the meridian, is therefore called the di- 

 rection of a stratum. This term is equally ap- 

 plied to strata at all the angles which deviate from 

 the vertical ; but as the tendency of the plane can 

 be truly discovered from the edge, only when that is 

 parallel to the horizon, the direction is determined 

 by an imaginary line at right angles to the incli- 

 nation, or parallel to the horizontal plane. 



In many cases of inclined strata therefore, as 

 the direction of the strata cannot be determined 

 by their elevated edges, but must be deduced from 

 their dips, the knowledge of the one is evidently 

 implied in that of the other. 



