MAGNETIC OBSERVATIOXS. 373 



fold. A long continuance of the disturbances, with the characteristic phe- 

 nomena attending deeper burial, beyond the point of coincidence, indicates 

 an anticlinal fold. A coincidence in both directions and the continuation of 

 the disturbances without diminution indicate an intrusive sheet. To these 

 may be added the delicate criterion which the unsymmetrical distances of 

 the horizontal maxima from the central zero may afford. If in the area 

 of separation the two belts depart from each so far as to be out of range of 

 each other's influence, and it is found on successive cross sections that the 

 nearest maxima are inside the lines of no deflection which directly indicates 

 the position of the rock, it can be concluded that the rocks dip toward each 

 other, and, on the other hand, if the nearer maxima are outside these lines, 

 that they dip away from each other. In the one case a syncline and in the 

 other an anticline would be indicated, and, of course, in either case it would 

 be certain that the phenomena could not be due to an intruded mass. 



