GEOLOGICAL EXPLOEATIOXS AND LITEKATUKE— 1S73. 55 



which we saw came to a iioiut at the Jackson iniuc, aud wideued to the west, so 

 the opposite croppiugs of this quartzite converge to the east and come togetlicr 

 at the Chocolate Flux quarry [on the shore of Lake Superior]. * * * From this 

 starting point the south rim of the basin bears away toward Goose Lake, where some 

 minor folds aud low dips make it the surface rock for a large area northeast of the 

 lake. From the south end of the lake west, the formation has a prevailing talcky char, 

 acter, often argillaceous and sometimes conglomeratic; it has a great thickness and 

 strikes west by south. West of the Cascade it seems to assume more the character 

 of a chloritic gneiss and protogiue, or at least a well-defined bed of i)rotogine rock 

 occupies the position in which we would expect to find the quartzite. 



The northerly rim, starting also from the Chocolate quarry, maintains a nearly 

 due-west course, crossing the railroad at Morgan Furnace, * * * passes north 

 of Teal Lake and south of Deer Lake, [is seen] occasionally at various points further 

 ■west, aud last, so far as I know, north of the Spurr Mountain, nearly 40 miles west 

 of Lake Superior. (Pp. 149-150.) 



The o-eueral geology of the entire district covered by his report is 

 described by Brooks in a chapter on the magnetism of the iron-bearing 

 rocks. This we quote: 



Kocks of the four oldest geological epochs yet made out on this continent are 

 represented on the Up])er Peninsula of Michigan; two belonging to the Azoic, one to 

 the Lower Silurian, and one between these, of questioned age. The equivalency of 

 these with the Canadian series has not been fully established, but the nomenclature 

 of the Canadian geologists will be employed provisionally. 



The Laurentiau of the Upper Peninsula is like that of Canada in being largely 

 made up of granitic gneisses, but differs in containing no limestone so far as I have 

 seen, and little, I may say practically no iron ore, and very little disseminated 

 magnetite. Next above the Laurentiau, and resting on it nonconformably, are the 

 Huronian or iron-bearing rocks; these are also called by the Canadian geologists 

 "the lower copper-bearing series." This series comprises several plainly stratified 

 beds of iron ore and ferruginous rock, varying in the percentage of metallic iron from 

 15 to G7 per cent, interstratified with greenish tough rocks, in which the bedding is 

 obscure, which appear to be more or less altered diorites, together with quartzites 

 (which pass into marble), clay-slates, mica-schists, aud various obscure magnesian 

 schists. The maximum thickness of the whole in the Marquette region is not far 

 from 5,000 feet. 



While the great Huronian area of Canada north of Georgian Bay bears, so far 

 as I am aware, little or no workable iron, and derives its economic importance from its 

 ores of cojiper, the Marquette series, supposed to be of the same age, are eminently 

 iron-bearing, and have as yet produced no copper. It is doubtful if in the same extent 



