372 THE CRYSTAL FALLS IRON-BBARIITG DISTRICT. 



in undiminislied vigor. Also, sucli intruded masses are seldom confined to 

 definite horizons for great distances and seldom split the formation into 

 symmetrical halves. Two nearly parallel lines of unequal strength, which, 

 as they are followed, become equal, and then again become unequal, with 

 the stronger on the opposite side, are often, therefore, characteristic phenom- 

 ena of this case. A good illustration of the unequal division of a magnetic 

 rock at different points along its strike by an intruded sheet which wedges 





ai 34 36 40 44 46 48 Z1 11. 48 V^iK »1 93 It 68 



'-''\\V\>: 



31 81 34 87 41 47 49 69 76 a8. 8^4 66 96 13 75 



ttfttff f* v\f N * » < !_ 



\ ■ A \ • 



35 »1 40 43 46 46 Jk-IJ ffi 68 h 17 63 62 



f f f r r f f i\^ I'y'-O >^ » *- 



\ \ 



39 36 41 49 48 48 6()\6,« J'S ?6 71 77 75 67 



' > ' tiff X f ^V^O V ^ ' ■ 



89 4.48 4;..fa8N7;\^ ^.. 78 M 



\ ' \^. 



44 4V 4^ 61 V' '80 '9 «« " 



' ' •' ' it J__J \ \.. 



\ _„. 



Fig. 24. — Magnetic map of a single formation split by an intruded sheet. 



out at both ends is given in fig. 24. Between the second find third trav- 

 erses from the north end the existence of this sheet has been proved by 

 drilling. 



4. SUMMARY. 



The means of discrimination among' these cases of convergence are 

 therefore founded on the deflections in the critical areas, where the separated 

 bands of magnetic material merge into one. Strong* deflections toward the 

 point where they run together, with a rapid disappearance of all disturb- 

 ances within a short distance of this point, indicate a pitching synclinal 



