GEOLOGICAL EXPLORATIONS AND LITERATURE. 47 



The n't'i'iTUco of tbf schistose sories of the reuoki.'O region to the Huroiiian is 

 justitied bytlie following cousiderations: (1) Tliere appears to be a direct continuation 

 with tlie iron-bearing system of the Marquette region of Michigan; (2) as sliown on a 

 subsequent iiage, the grand subdivisions of the lja<l river and Marquette systems 

 both show tlie same relation to the Laureutiau and Keweeuawan systems as found in 

 the Huronian of Canada; i. e., are newer than the former and older than the latter; 

 (4) the Marciuette system is found in unconformable contact with the Lower Silurian 

 red sandstone of lake Su])erior. The Mariiuette Huronian, in its southerly extension 

 in the Menominee region, is also found in unconformable contact with the fossilifer- 

 ous primordial sandstone of the Mississippi valley, a fact which, even if the evidence 

 were not amply sufticient without, would demonstrate the futility of the attempts 

 made by some to refer the whole series of lake Superior crystalline rocks to the 

 Silurian. (Pp. 5-7.) 



The general succession of formations in northern Wisconsin, from 

 above downward, is held to be as follows: (1) Lake Superior Sandstone; 

 uncouformably followed by (2) the Copper-Bearing- or Keweenaw series ; 

 unconformably followed by (3) the Iron- Bearing or Huronian series; un- 

 couformably underlain in its turn by (4) the Gneissic or Laurentian. In 

 support of the belief that there is an unconformity between the Kewee- 

 uawan and Huronian series, Brooks's arguments, already noted above, are 

 quoted and indorsed, after which the author proceeds as follows : 



I conceive that fiuther evidence of nonconformity is afforded in the Wisconsin 

 region by the following facts: (1) In the Penokee country tlie uppermost beds of the 

 Huronian are gradually cut out, as we trace them westward, by the gabbro that forms 

 the base of the Keweeuawan series, a fact which appears to me best explained by 

 the supposition that the gabbro covers and conceals these missing beds. (2) There 

 is not an absolute uniformity in dip between the Huron iau and Keweeuawan rocks 

 in this region, the latter standing connnonly at a higlier angle. (3) West of lake 

 Numakagon the diabases and other eruptive rocks of the Keweenaw series api)ear to 

 conq)leteIy cover tlie Huronian in a great overflow. Nevei'theless, the approach to 

 conformity in Wisconsin is close, and were we to draw our conchisions from tliis 

 region only, the nonconformity could hardly be regarded as proved. There are no 

 sudi inidulations in the Huronian of the Penokee district as in Michigan, tlie subor- 

 dinate mendiers making long and regular bands conforming to the general trend of 

 the formation, and also, in a general way, to the trend of the several belts of the 

 Keweenaw series. Moreover, the lessening in dip toward tlie west, already noted as 

 affecting the latter rocks, is observed also in the underlying Hui'ouiau so far as these 

 can be traced westward. (P. 22). 



