250 i?. D. Irving — Is there a Huronian Group ? 



words, there is good reason to believe that all of these areas 

 were once connected, the connections having since been re- 

 moved by erosion. Hence the correlation of these different 

 areas by lithology, stratigraphy and structural relations to ad- 

 joining groups is not so entirely unlike the use of these same 

 criteria in tracing one of the fossiliferous groups from point to 

 point. 



Proceeding westward now from the type Huronian area, all 

 the pre-Cambrian rocks are concealed, either by the waters of 

 Lake Superior or by the overlying horizontal formations of the 

 eastern part of the Upper Peninsula of Michigan, until the 

 vicinity of Marquette, on the south shore of the lake, is 

 reached. Here a belt of much crumpled, generally steeply in- 

 clined and partly schistose strata reaches the lake coast, with 

 a width on the shore line of about five miles. The coast of 

 the lake here has a nearly due northerly trend, facing eastward. 

 The course of the rock belt referred to is at right angles to 

 this, that is, it lies east and west. Followed westward the belt 

 is found at first to expand to a width of some twelve to 

 fifteen miles, and then to contract again, until at the eastern 

 end of Lake Michigamme, thirty miles west of Lake Superior, 

 it is little more than two miles wide. Still farther west it ex- 

 pands over a large area, whose limits can hardly be said to be 

 as yet determined. 



North and south of this belt are large areas of granitic and 

 gneissic rocks. Two widely divergent views have been held 

 with regard to the relations of these granites to the schists be- 

 tween them. The earlier writers on the region, and especially 

 Messrs. Foster and Whitney, in their classical report, held that 

 the granites were of eruptive origin, and of a date subsequent 

 to the formation of the various stratiform rocks, whose crum- 

 pled and disturbed positions these geologists were disposed to 

 assign to the eruption of the granite masses on either side of: 

 the trough. Later, on account of the arguments of Kimball, 

 Murray, Brooks, etc., the view came to be generally held that 

 the granitic and gneissic rocks represented the ancient Lauren- 

 tian basement, upon which all of the stratiform or Huronian 

 rocks were deposited unconformably ; that, the whole region 

 having been subsequently affected by a lateral pressure, the 

 sedimentary rocks were pushed into folds, and that the granitic 

 rocks on either side were brought to the surface by denuda- 

 tion. Recently the older view of Foster and Whitney has been 

 advocated by Dr. M. E. Wadsworth* and Dr. 0. Rominger,f 

 both supporting it by an appeal to intrusions of the schistose 



* Bulletin Mus. Comp. Zool., vol. vii, No. 1, 1880. 

 f Geological Survey of Michigan, vol. iv. 



