THE ARCILEAN EOCKS. 465 



tions on this region are still in progress, and such generalizations 

 would now be premature. Attention may be drawn, however, to the 

 fact that the general directions of the strikes preserve a sort of paral- 

 lelism to the sides of the somewhat irregularly shaped Archaean area. 

 Thus, on the Wisconsin, Wolf, 1 Peshtigo 2 and Oconto, 8 the strikes 

 are northeastward, coinciding with the long boundary line on the 

 southeast side; on the Black, Yellow, and lower Chippewa, the di- 

 rections are northwestward, corresponding in general to the south- 

 western boundary line; on the upper Chippewa, and in the Penokee 

 region, the strikes are generally north of east, corresponding with the 

 Lake Superior side of the Archaean area. Whether this correspond- 

 ence has any significance or not, remains to be seen. It is quite pos- 

 sible that the northwestward strikes of the Black, Yellow and lower 

 Chippewa indicate the existence of a continuous band of Huronian 

 (including then gneissic rocks and granites) which, curving around to 

 the north and northeast, includes the quartzites of Rice lake, in Bar- 

 ron county, and joins finally with the Iron Range series of Ashland 

 county. The remaining northeastward strikes, on this view, would 

 be those of the original Laurentian nucleus. 



It has already been said that most of the rocks of the main Archaean 

 area are referred to the Laurentian. This is done partly because of 

 their general lithological characters, but more especially because 

 they are found near Lake Superior, and also near the Michigan bound- 

 ary, in Oconto county, underlying unconformably other metamorphic 

 beds, chiefly of a slaty character, which, from their relations both to 

 the Copper-bearing series and Silurian sandstones of Lake Superior, 

 and to the Potsdam sandstone of Central Wisconsin, quite evidently 

 occupy the horizon of the Canadian Huronian. When these relations 

 are taken into account with their great resemblance in lithological 

 characters to the typical Canadian formations, from which they are 

 but little removed, and with which they are indeed quite probably 

 continuous underneath the waters of Lake Superior, the reference of 

 the two Wisconsin series of crystalline rocks to the Laurentian and 

 Huronian seems unavoidable. 



The undoubted Huronian beds of Wisconsin lie entirely without 

 the district which is the object of the present report. Those lying 

 within the district, on Black and Yellow rivers, already alluded to as 

 doubtfully Huronian, are as yet too doubtfully so to merit further at- 

 tention in this place. 



The only materials of economic importance yet known to occur 

 in the Archrean of Central Wisconsin are kaolin or rotted rock, and 



1 Manuscript report, E. T. Sweet. * Oral communication, T. C. Chamberlin, 

 Wis. SUB. 30 



