Iron Ore Ranges of Minnesota. 53 



the graywackes, or comprises a large proportion of them. Such a 

 rock has been called "greenwacke." Sometimes the green schist is 

 permeated by fine chemical, yet granular, quartz. Sometimes the 

 chloritic element in the schist is rather micaceous, with a silky 

 luster, but having still a light green tint. Sometimes the whole 

 formation is converted to a metamorphic rock, forming mica schist, 

 gneiss, hornblende schist and related rocks. This condition usually 

 extends to the formation of granite, syenyte, dioryte and a number 

 of massive igneous rocks, which are seen to penetrate the original 

 rocks as dikes. When the greenstone itself is thus affected by 

 metamorphism and fusion it seems to have given rise to diabase and 

 gabbro, which also can be seen to pierce the original rocks in all 

 directions and which sometimes overflowed at the surface, forming 

 traps. 



Now this eries of rocks with their variations, as a whole, can- 

 not be found outside of the Archean. They cannot be found in the 

 Mesabi formation. 



G. The Vermilion range ore. 



If we note specially the ore of the Vermilion range, we are at 

 once impressed with the fact that it is a "hard" ore. This is ex- 

 hibited at Soudan, its chief impurity being quartz. It is a charac- 

 teristic red hematite. The ore at Ely, as exhibited at the Chandler 

 mine, you may consider an exception, as it was called a "soft" ore. 

 But it is no exception. It was at first in the form of hard jaspilyte 

 as at Soudan. It had been crushed into small pieces, but each 

 piece was hard as the Soudan ore. This shattered condition of 

 the Chandler ore was due, probably, to movements of the earth's 

 crust, caused by earthquakes. It is to be remembered that an 

 enormous lapse of time passed between the formation of the ore 

 and the close of the great Keweenawan age, and that during the 

 Keweenawan age northern Minnesota was convulsed by the most 

 profound earthquakes and by volcanic action. 



7. Two parts in the Archean. 



1 have mentioned already the division of the Archean into two 

 parts, the Lower Keewatin and the Upper Keewatin, and the exist- 

 ence of . jaspilyte also in the upper member. These two great 

 parts are entirely similar in composition and in pose\ but they 

 are separated by a great conglomerate, the Ogishke conglomerate, 

 which belongs in the basal part of the Upper Keewatin and marks a 

 great nonconformity between the two parts. Aside from the exist- 

 ence of this great conglomerate, it seems as if the processes of 

 rock making continued the same from the Lower Keewatin through 

 the Upper Keewatin. What may have been the cause of this great 

 conglomerate is entirely problematical, but it has been suggested by 

 Prof. Coleman that it is of the nature of a glacial moraine, which, 

 if true, would carry glaciation back almost to the commencement of 

 geological time. 



S. The Mesabi Iron Range. 



I have now described in a very synoptical and Incomplete man- 

 ner the Vermilion Iron range, its rocks and its ore. We turn now 



