48 THE PENOKEE IRON-BEARING SERIES. 



IbvinCt (R. D.). Geology of the Eastern Lake Superior District. In Geology 

 of Wisconsin, vol. iii, Pt. 3, ]ip. 51-238, with 6 atlas plates, 18 vohiiuc plates 

 (including 7 colored microscopical plates), and 4 figures. 



This is a detailed account of the geokigy of that portion of northern 

 Wisconsin which is (b'ained by the waters of Bad and Montreal rivers and, 

 of course, covers all that portion of the belt now to be studied, which lies 

 west of the Montreal river. The chapter titles are as follows: Introduc- 

 tion, Topography, The Laurentian System, The Huronian System, The 

 Keweenawan or Copper-Bearing System, The Lake Superior or Potsdam 

 Sandstone, The Quaternary Deposits, Appendices A and B. Tlie chapters 

 on the Huronian and Laurentian are of chief interest in the present con- 

 nection. From the former chapter we quote: 



The Iluronian rocks lie together in a narrow belt fi'oni half a mile to 3 miles in 

 widtli, which stretches entirely across tlie district, from the west line ot"T. 11, R. 5 W., 

 to tlie .Alichigan boundary at the Montreal river, in Sees. 2-1 and 13, T. lr(i, R. 2 E. 

 The total length of tlie belt in this distance is about -16 miles. The wider portions 

 are toward the east, the western part uarrowing in places to as little .is a mile or 

 even half a mile in width, as in the sections just south of Bladder lake. The total 

 area underlain by these I'ocks is just about 100 square miles. (P. 100). 



Then, after giving in Ijrief the course of the Huronian belt through the 

 various townships and sections, the report proceeds: 



The southern boundary of the Iluronian, oi' its Hue of junction with the Lauren- 

 tian, is a very sharply defined line, on account of the bold topography and frequent 

 rock exposures of the Penokee range. Even in that portion of the Iluronian belt 

 where tlie Penokee range disappears, and the rocks are entirely concealed by drift 

 and swamps, the magnetic attraction exerted by the iron-bearing member of the 

 formation, one of its lower layers, serves to fix very closely the southern boundary. 

 On the accomi)anyiiig atlas jdales this boundary line is laid down so accurately and 

 the liicts ujion which it is based are there detailed so fully that no further exjilauatiou 

 is needed here. 



In addition to the facts given on the maps and in the details of the following 

 liages, it is merely necessary to say here, with regard to tlie northern boundary, that 

 it does not follow the strike of the Huronian beds, but cuts across them in a more or 

 less irregular way. The width of the Huronian does not vary on account of the 

 thickening or thinning or disai)pearance of any of its subordinate layers, but the 

 wider portions include higher layers, which are wanting in the narrower iiortions. 

 The iTregularity, then, of the northern boundary is due to a nonconforniity of the 

 overlying rocks with the Huronian. It should also be said that these overlying rocks, 



