Position of Strata in Stratified Rocks. 371 



Fig. 4. 



Fig. 4. shows the operation which takes place, in case of the true 

 direction of the strata being one of the given lines of stratifica- 

 tion, or seams, in such a case where the angle made by this line 

 with its horizontal projection 0, the process is much simplified, 

 although always carried on according to the same principle. The 

 same letters being used in all the four figures, to denote the ana- 

 logous points, the explanation above given will apply to them 

 all. 



Although this last way of resolving the problem did not re- 

 quire any more precise data than those which the less skilled ob- 

 server can easily obtain in confining himself to the simple use of 

 the compass and the plumb-line ; and although this proceeding 

 requires but a little attention, and the use of the most elementary 

 processes of geometry, it is nevertheless to be feared that the 

 practical geologist, to whose care the solutions of such often im- 

 portant problems are trusted, would often think it too long and 

 too complicated a method to be prevailed upon to use it. 



Such an idea, and at the same time the wish that numerous 

 and accurate observations of the position of the strata should be 



VOL. XII. PART II. B b 



