GEOLOGY IN IS^ORTHERi^ WISCONSIls'. 55 



In Michigan, and in all regions where magnetic ore is found 

 much reliance in exploring is placed upon magnetic surveys. Val- 

 uable mines have been discovered by noting the abnormal deflec- 

 tion of a delicate magnetic needle in crossing the formation at 

 right angles to its trend. This method often succeeds when the 

 dip compass fails. Although magnetic surveys have not been made 

 in the region under consideration, linear surveys have, and the va- 

 riation at several points upon each section recorded upon the town- 

 ship plats. In the township through which the Huronian belt is 

 supposed to pass, the difference between the maximum and mimi, 

 mum deflection of the needle from the magnetic meridian is much 

 greater than in townships known to be distant from local magnetic 

 influences. For instance, in township 37, range 20 west, the dif- 

 ference is 5 degrees, 30 minutes. Numerous other examples might 

 be mentioned. The fluctuations of the needle from a fixed point 

 under ordinary circumstances, and in ordinary townships, is not 

 usually over one or tv/o degrees. Investigations with a dip com- 

 pass, and with an instrument for making accurate m.agnetic sur- 

 veys, will certainly settle the question of the western prolongation 

 of the magnetic schists. It will be necessary to go over a consid- 

 erable portion of Burnett county, the southwest of Ashland, and 

 southeast of Bayfield, and possibly the northern part of Polk very 

 carefully. It is an important question, worthy of thorough inves- 

 tigation, and one which should be definitely decided as soon as pos- 

 sible by the Geological Corps. 



