GEOLOGICAL EXPLORATIONS AXD LITERATURE. 37 



In short, we see nothing here, nor indeed anywhere in the lake 

 Superior country to warrant the \4ew that the Iron-bearing- or Huronian 

 series has an uppermost granitic member. Tlie Menominee granite belt we 

 look on as lielonging to the great basement gneissic formation ; the Penokee 

 granite belt is really a great gabbro area, in which occur isolated and limited 

 intrusions of granite, gl■aniti^ porphyry, and allied acid rocks. This 

 gabbro, with red acid eruptions, finds its exact equivalent as to stratigraph- 

 ical position and associated intrusions in the great gabbro belt which forms 

 the bold range of hills at Dulutli, and stretches thence far to the northeast- 

 ward into the interior of that portion of Minnesota which lies north of lake 

 Superior.^ 



Brooks (T. B.). Classified List of Rocks observed in the Huronian Series 



« 



south of Lake Sui)eiior. Am. Jour. Sci., 3d series, vol. xii, 1876, pi*. 194-204. 



This paper, as its title indicates, is an attempt at a lithological classifi- 

 cation of all the varieties of rocks oljserved liy Brooks in those formations 

 on the south side of lake Superior, which he regarded as the equivalents 

 of the original Huronian of the north shore of lake Huron. It also erives 

 a taljle showing the "sequence of Huronian strata at several points near 

 lake Superior, with hypothesis of equivalency." Tlie districts referred to 

 in tliis table are (1) the north shore of lake Huron, (2) the Marquette Iron 

 district, (3) the Menominee Iron district, (4) the district of Black river, 

 Michigan, and (5) the district of Bad river, Wisconsin. The last two dis- 

 trict are within the area now under description, and we therefore quote the 

 table so far as it gives the succession of strata for Black and Bad rivers. 

 "We do not now discuss Brooks's hypothesis of equivalency for these 

 sections with those of the other districts refeired to. We need merely to 

 say that we can not accept his scheme in many respects. Indeed, we filid 

 ■too many things that we can not agree with in his succession for the 

 Penokee-Gogebic series itself to allow us to accept any scheme of equiva- 

 lency based upon it. His Bad river section is particularly imperfect, there 

 being great thicknesses of rock omitted entirely, while the granite belt 



'Am. Jour. Sci., 3(1 series, vol. xi, 1876, p. 49.S; Geol. of Wis., vol. iii, 1880, pp. 10, 13, 22, 35, 

 44-46, 145-149, 167-183, 193-195, 233-2.37; ami atlas plates xxi, xxii, xxiv. xxv, xxvi, xxvii ; Monograph 

 U. S. Geol. Survey, vol. v, 1883, pp. 37-57, 56-58, 144-145, 155-157, 158, 230-238, 266, 268-275. 



