GENERAL GEOLOGY OF THE DISTRICT. 441 



a transit survey made bv Mr. J. Parke Clianniiii;-, takiiii;- as tlie pciints of 

 measurement the junctions between the vitreous quartzitcs and the over- 

 lying ferrug'inous rocks on the east and west sides of tlie river. 



FaiiK in tlic Eastern area. — In chapter viii, p. 424, it lias l)een suggested 

 that there is a fault in tlie east side of T. 47 N., R. 44 W., Michigan, run- 

 ning: in a diao-onal direction from the southwest corner of Sec. 25 to a short 

 distance west of the east quarter post of Sec. 13. The rocks west of this 

 line have probably been thrown south of the corresponding la^'ers to the 

 east, thus explaining part of the discordance in the rocks of the iron 

 formation, as well as the diflference of one4ialf mile in the southern bound- 

 ary of the Keweenaw rocks in the eastern y^art of the townshij), and also 

 lessening the thickness of the Penokee rocks in this locality, l)ut as the 

 probability of this fault and its structural relations have been fidly treated 

 in the chapter referred to, the subject will not be further discussed here. 



At all of these places the ground between the exposui-es is covered on 

 the ea.st and west sides of the fault lines, so that it is not ])ossible to accu- 

 rately locate them. As is common, the broken layers have readily yielded 

 to erosion and the fault lines in two cases have been utilized by the drain- 

 age system of the district. 



SECTION II.— STRUCTURE.! 



The Southern Complex. — The subject proper of this memoir is the con- 

 formable succession of rocks whicli contains the Iron-bearing member, 

 and has therefore often been called the iron-bearing series. It has often 

 been necessaiy to allude to the,series south and nortii. The latter series 

 has not ])een given a separate chapter, for the varie<l rocks there found 

 are parts of the great Keweenaw series which has already l)een treated in 

 a separate memoir.- In chapter ii the former re)cks have lieen described 

 in sufficient detail to compare them in their structural features and litho- 



' The separability of the Penokee series from the Southern Comple.x and tlic Keweenaw series 

 by means of unconformities has been maintained by Prof. Irviu;;; iu several of Lis publieations. (See 

 Literature, Cliap. I.) As to these geueral relations, the only thing- added is new evidence supporting 

 these positions. 



^Copper-bearing rocks of Lake Superior; by R. D. Irving, U. S. Cieol. .Survey, Monograph v. 



