R. D. Irving — Is there a Huronian Group f 255 



and schist occur in the slate or quartzite at the contact. The 

 occurrences on the S.E. \ of Sec. 29, T. 48, R. 25 W., only 

 about three miles west of Marquette, and those in Sec. 22 and 

 adjoining sections of T. 47, R. 26 W., south and southwest from 

 Goose Lake, are very striking; but possibly those in sections 8 

 and 19 of T. 49, R. 28 W., in the vicinity of Silver Lake, are 

 yet more so. In this vicinity the older rocks, consisting of 

 granite and schists involved with one another in such a way as 

 to render irresistible the conclusion that the granite has in- 

 truded the schists, form a bold range sloping abruptly down to 

 a lower area occupied by the softer detrital rocks. At the foot 

 of the granite range the detritals, in contact with the granite 

 and schists, are found crowded with fragments of both, of all 

 sizes, up to pieces several feet across. The fragments are 

 partly angular, lying in a breccia against the granite, and 

 partly well-rounded. Since the granitic fragments repre- 

 sent a rock which, according to the present state of litho- 

 logical science, could only have formed at great depths, 

 and since the schists, whatever their first origin, must 

 have received immense alterations by pressure before yield- 

 ing fragments, we are forced to believe in a period of extended 

 sub-asrial erosion intervening between the times of first forma- 

 tion of the older and newer rocks. 



If we proceed in a direction southward from the Marquette 

 region, we traverse great areas underlain by the granites, 

 gneisses and schists of the older formation, but when the 

 Menominee Eiver is reached, at the boundary of Wisconsin 

 and Michigan, we have crossed also at least four distinct belts 

 occupied by the rocks of the newer or iron-bearing series. 

 According to the mapping of the Michigan geologists these 

 several belts merge, farther westward, into a single extended 

 area of the iron-bearing series. It seems certain that this for- 

 mation has a wide spread in that direction, but just what the 

 relative extents of the older and newer rocks in this direction 

 are, remains to be shown by further exploration. Of the several 

 belts crossed by a line running south from the Marquette 



/7*o7v Jfeasvrvt 



GrcaUte " Cryttivtlwoi-. <S otvCsts- '" GrccrvLte 



FiQr. 5. Generalized ideal section of the Menominee Iron Kegion. Scale, 3 miles 



to the inch. 



belt to the Menominee River, that one skirting the Me- 

 nominee River on its northern or Michigan side and run- 



