364 



THE CEYSTAL FALLS lEON-BEAEING DISTEIOT. 



of the former case, and tlie result of the interaction of the two legs is to 

 increase the numerical values of these, as well as to bring them nearer 

 together. It is evident that the deflections of the horizontal needle in this 

 case could hardly be distinguished from those that would be produced by a 

 single vertical formation buried to a considerable depth. 



Let it next be supposed that the two rocks dip toward each other at 

 different angles, the strikes remaining parallel, and also that the rock of 

 lower dip is buried to the greater depth. This, then, is a case in which the 

 magnetic effect of one limb of the syncline is much stronger than that of 

 the other. 



In PL XL VIII, fig. 7, the curves of the two components are given for 

 the special case in which the right-hand limb of the synclinal dips at an 

 angle of 90°, and has a surface covering 7^=2, while the left-hand limb 

 dips at an angle of 26° '34', and has a surface covering /i=4. It is interest- 



Fig. ]9 — Truncated 'anticlinal fold witli gently dipping limbs. 



ing to compare the theoretical results of this figure with the curves of PI. 

 XLVIII, fig. 8, which represent deflections actually observed, and not 

 components. 



In the latter figure the strike of the two rocks is represented by the 

 heavy lines. The two rocks are the same formation, brought up by folding 

 on opposite sides of a synclinal trough. The synclinal is slightly pushed 

 over, so that the eastern rock dips nearly vertical, while the western has a 

 much lower dip toward the east, and is also more deeply buried. These 

 facts rest on independent evidence, yet they might all be inferred from the 

 observations recorded in this fig'ure. 



The dip curve in this case shows two distinct maxima, a smaller under 



