458 GEOLOGY OF CENTRAL WISCONSIN. 



and eastern borders of the main Archaean mass. There is no proof 

 at hand that the rocks of these patches are unconformably super- 

 posed npon Laurentian strata, but the contrast between them and the 

 Laurentian gneisses and schists, their resemblance to Huronian rocks 

 elsewhere, and more especially the parallelism just referred to, strong- 

 ly suggest the possibility of their forming part of a continuous band 

 of Huronian, of which the Lake Superior and Oconto areas are other 

 portions, encircling the Laurentian core, after the manner of the later 

 and undisturbed Silurian accumulations. Regarding the Black river 

 ferruginous schists, and the associated gneisses as Huronian, a continua- 

 tion of the same belt, completing the circuit, may possibly exist in 

 the northwestward trending gneissic and hornblendic beds of the low- 

 er Chippewa, 1 the arenaceous and conglomeratic quartzite of the hills 

 in T. 32, R. 7 "W., near the Chippewa river, 2 and the quartzite and 

 associated pipestone of Rice Lake, in Barron county. 3 This idea of 

 a continuous Huronian belt encircling a Laurentian core is thrown 

 out as a suggestion only, a generalization towards which the facts in 

 my possession at this writing would seem to point. At present all 

 that we can affirm with any degree of certainty of the great crystal- 

 line rock area of northern Wisconsin is that most of its rocks are 

 Laurentian, that on its northern a'nd northeastern edges are some un- 

 doubted Huronian beds, and that on its southern and southwestern 

 borders are again rocks between whose Laurentian and Huronian age 

 there remains some question, although they quite probably are to be 

 assigned to the latter period. 



From its northeastern corner the Wisconsin Archaean nucleus, in- 

 cluding now both Huronian and Laurentian rocks, sends a long pro- 

 jection across the Upper Peninsula of Michigan to the shores of Lake 

 Superior, possibly connecting, beneath the lake, with the great Cana- 

 dian Archaean area. Thus, from the earliest Paleozoic times, the rock 

 depositions skirting the Archaean of Wisconsin on the east, south and 

 west, must have gone on independently of those on its northern side. 

 The outcrops of the undisturbed and unaltered Silurian formations, 

 which succeed one another in receding concentric bands on the east- 

 ern, southern and western sides of the Archaean of Wisconsin, are the 

 direct continuations of the outcrop bands of a series of strata, which, 

 after following the southern side of the Canadian Archaean westward 

 through New York and Canada, make a great curve to the northward 

 across the peninsula between Lakes Huron and Erie, and also across 



1 E. T. Sweet, manuscript report and also Transactions Wis. Acad. Sci., Vol. III. 



2 E. T. Sweet, Loc. cit. 



3 Owen's Geological Survey of Iowa, Wisconsin and Minnesota. 



