340 THE VERMILION IRON-BEARING DISTRICT. 



METAMOKPHISM OF THE KNIFE LAKE SLATES. 



The rocks possessing- the characters briefly described above are those 

 which we may call the normal Knife Lake slates. Even these so-called 

 normal slates have been very much metamorphosed. The metamorphism 

 has been caused by the infiltration of material (chiefly silica and calcium 

 carbonate), by the cementation of the particles by these substances, and 

 by the further .cementation of the rock by chemical changes of the 

 fragments, which produced new minerals and also caused the secondary 

 enlargement of the old mineral fragments. These rocks show locally the 

 effect of orogenic movements in more or less well-developed schistose 

 structure and fracturing. 



At several places in the district the slates are in contact with later 

 igneous rocks, both acid and basic, and have been metamorphosed by the 

 intrusion of these rocks. In all cases the rocks, as stated above, have 

 been affected by processes of cementation and to a certain extent by 

 orogi'aphic movements, and in some instances these sediments have been 

 metamorphosed by acid intrusives and then have been acted upon by the 

 great Keweenawan gabbro and still further changed. Hence it is exceed- 

 ingly difficult to discriminate between the kinds of metamorphic products 

 which are due to each one of these agencies. In the following paragraphs 

 a brief description will be given of the macroscopic characters of those 

 Knife Lake slates which have been metamorphosed by the contact action 

 of the acid and basic intrusives, and which occur in the four most important 

 areas: (1) South of Tower, along- the Duluth and Iron Range Railroad, near 

 milepost 92; (2) on the Kawishiwi River; (3) at Snowbank and Caca- 

 quabic lakes; and (4) in the vicinity of Gobbemichigamma and Paul lakes. 



Contact effect of the granite. — The sediments metamorphosed by the 

 Griants Range granite are well exposed near milepost 92 on the Duluth 

 and Iron Range Railroad, south of Tower, and this place is readily 

 accessible. They are also well exposed on the Kawishiwi River, near the 

 mouth of that river where it empties into Farm Lake ; along the shore east 

 thereof; and on the portage leaving the bay of the river, in the SE. \ of sec. 

 30, T. 63 N., R. 10 W., leading southeast to Clearwater Lake. In places 

 some conglomerates occur, especially on the islands' in the river in sec. 26, 

 T. 63 N., R. 11 W., but the coarse sediments are very subordinate. The 



