GEOLOGICAL EXPLOEATIONS AND LITEEATUEE. 33 



JuLiEN (Alexis A.). Litliological DeseiiiitioiKS, etc., of -59 specimens of the 

 Hurouiau aud Laiireutiau Kocks of tlic Upper reiiinsula, appendix A, Geological 

 Sui-vey of Michigan, New York, 1873, vol. ii, pp. 1-197. 



This report contains uonmicroscopic litliological descriptions of a few 

 rock specimens collected by T. B. Brooks and R. Piiinpelly in the Gogebic 

 region in 1871, during the trip already several times referred to. 



1874. 



Irving (R. D.). On the Age of the (Jopi)er- bearing Rocks of Lake Superior; 

 and on the Westward Continuation of the Lake Superior Synclinal. Am. Jour. Sci., 

 3d series, vol. viii, 1874, pp. 46-56, with a map aud section. 



This is a paper giving an account (if several conclusions reached after 

 a first season's work in the Bad river country of northern Wisconsin. Its 

 main object is to set forth conclusions on the points indicated in the title. 

 The following paragraphs are quoted as bearing on the district which forms 

 our present subject: 



2. The Huronian rocks (II on the map and section), which directly overlie th<> 

 LaUrentian, and unconffirmably, as shown by Brooks and Pumpelly from observations 

 made by them in Michigan just east of the Wisconsin line, constitute in Ashland 

 county a continuous narrow belt, whose central portion is the well known "Penokie 

 Iron range," and whose width never exceeds 2 miles, being usually much less than 

 this. Tliis belt extends without break into Michigan, almost as far as lake Gogebic, 

 where the rocks are lost sight of, being covered bj^ accumulations of drift, and finally 

 by horizontal Silurian rocks. Tliey do not reajipear until, 100 miles farther east, the 

 Marquette iron region is reached. Here they are found again, with some important 

 changes and covering a much wider extent of territory. Toward its western extremity 

 the Huronian belt appears to come to an abrupt ending, the underlying Laurentian 

 and overlying Copper-bearing series coming together. Farther west, however, just on 

 the west side of Ashland county, are two isolated belts of these rocks, in every way 

 similar to tlie main area, each having in the same manner its central ridge. As to 

 the continuation still farther westward of the Huronian, nothing whatever is known, 

 as is indicated on the map by an interrogation point. The rocks of this group iu 

 northern Wisconsin are siliceous schists, talco-siliceous schists, black slates of unde- 

 termined comitosition, white quartz rocks, quartzites, magnetic and specular schists 

 of various kinds, nmguetic and specular iron ores, diorites, diorite slates, and diorite 

 schists. The beds of one portion of the group, about 500 feet in actual thickness and 

 continuous for over .30 miles, are impregnated tlu'oughout with the specular and mag- 



MON XIX 3 



