416 THE CRYSTAL FALLS IRON-BEAEING DISTEIOT. 



outcrop in the western part of section 36. Near the center of section 36 

 another line, marking' the western end of the Grroveland synchne, begins 

 and continues for a mile and a half east to the eastern portion of sec. 31, 

 T. 42 N., R. 29 W. Along the western portion of this line are many test 

 pits, and in section 31 the fine exposures of the Grroveland hill. 



Four hundred paces north of the center of sec. 32, T. 42 N., R. 29 W., 

 another line of attraction begins, and may be followed toward the east 

 without interruption nearly to the east line of section 33 of the same town- 

 ship. Along this line, which is comparatively feeble and crosses wet 

 ground, there are but few test pits. In the eastern part of section 33, 

 beyond the point at which the attractions cease, many pits have been sunk 

 to and into the Mansfield formation, which is there somewhat ferruginous. 

 From this point east for 4 miles the Grroveland formation has not been 

 recognized. . 



In the northern part of sees. 32 and 33, T. 42 N., R. 28 W., the fer- 

 ruginous rocks are again well exposed on Felch Mountain for nearl)^ a mile 

 along the strike, and may be identified for half a mile farther by the vigor- 

 ous disturbances produced in the magnetic needles. In the southeastern 

 quarter of section 33 the Groveland formation is again encountered in a 

 small and much-disturbed area, in faulted contact with the Archean. 



The most conspicuous hills within the Algonkian belt owe their relief 

 to the fact that they are underlain by the Groveland formation, but else- 

 where this formation has left but little impress on the topography, perhaps 

 because the local base-levels are cut nearly to the bottoms of the synclines 

 in which it is preserved. The two hills referred to — Felch Mountain, in 

 sees. 32 and 33, T. 42 N., R. 28 W., and the Groveland hill, in sec. 31, 

 T. 42 N., R. 29 W. — stand 100 feet or more above the average level of the 

 surrounding Algonkian territory, and in both instances the infolded second- 

 ary synclines are exceptionally deep and broad. The magnetic lines which 

 indicate the other synclines pass through low ground, and the belts of dis- 

 turbance are much narrower than in the cases of the two principal hills. 

 • There seems to be, so far as the collected material warrants a judgment, no 

 lithological difference between the rocks of the narrow and those of the 

 broad and deep synclines, and accordingly the relief of the latter is believed 

 to be caused by their depth below the adjacent base-levels and not by their 

 more resistant character. 



