It. D. Irving — Is there a Huronian Group ? 365 



Akt. XXXIX. — Is there a Huronian Group? by R D. Irving-. 



[Continued from page 263.] 



VI. North of the northern limit of the Animike' beds, slaty 

 and schistose rocks form a belt which extends from Vermillion 

 Lake in an easterly and north of east direction to the national 

 boundary line in the vicinit}^ of Knife and Saganaga lakes, a 

 distance of some 60 miles. To the west of Vermillion Lake 

 this belt has been traced for some miles, but is soon lost under- 

 neath the heavy glacial accumulations of that region. To the 

 north the schists become involved with granitic and gneissic 

 rocks. A similar area of granite and gneiss bounds the schis- 

 tose belt on the south, over much of the distance, and here also 

 are seen again the intricate intersections of the schistose rocks 

 by the granite. After reaching a point some thirty miles east 

 of Vermillion Lake, however, the great fiat-lying mass of gab- 

 bro which lies at the base of the Keweenaw Series of that 

 region overlaps and conceals this granite, the overlap extend- 

 ing over to the schistose belt itself. Another granite area lies 

 directly athwart the course of the schists in the vicinity of 

 Saganaga Lake, although a portion of the schist belt apparently 

 continues farther to the northeastward into Canada along the 

 northwestern side of this granite. 



Folding and the production of a schistose structure by 

 lateral pressure seem to have been pushed to the very last ex- 

 treme among the rocks of this slate and schist belt, the dips 

 within which are generally close to vertical, although here and 

 there among some of the fragmental rocks of the belt, close 

 crumplings may be traced with their sharp anticlinal and syn- 

 clinal bends. The secondary schistose structure, with its 

 accompanying metasomatic changes has been developed to the 

 highest degree among the rocks of eruptive as well as among 

 those of sedimentary origin. The common structural directions 

 of all the rocks of the belt, as to both strike and dip and the gen- 

 erally prevailing schistose structure, suggest at first the con- 

 clusion that all of the schists of the belt are part of one forma- 

 tion ; or, if of two formations, that the distinction between the 

 two is no longer recognizable. 



A closer study, however, serves to render such a conclusion 

 less evident ; and shows that we have among the rocks of the 

 belt two types, in one of which the crystalline structure is com- 

 plete, and in which there is little or none of an original frag- 

 mental texture, while in the other the fragmental texture is 

 still distinct and the alteration has progressed to a smaller 

 degree. Associated with the latter, slaty rather than schistose, 



Am. Jour. Sol— Third Series, Vol. XXXIV, No. 203.— Nov., 1887. 

 24 



