ILLUSTEATIONS. XITT 



FlG.12. Sketch illustrating contortion of Upper Huronian strata - 179 



13. Sketch showiug change of strike of Upper Huroniau beds, clue to the folds 179 



14. Sketch to illustrate the occurrence of ore bodies 182 



15. Magnetic cross section in T. 45 N., R. 31 W 345 



16. Circles of attraction 



346 



17. The forces acting on the dip needle 3''^7 



18. Curves showing the relations between the horizontal components at the points of maxi- 



mum deflection, for rocks dipping at various angles and buried to various depths 354 



19. Truncated anticlinal fold with gently dipping limbs 364 



20. Truncated anticlinal fold with steeply dipping limbs.-. 365 



21. Plan and cross sections of a pitching syncline 367 



22. Magnetic map of the Groveland Basin 370 



23. Plan and cross sections of a pitching anticline 371 



24. Magnetic map of a single formation split by an intruded sheet 372 



