Iron Ore Ranges of Minnesota. ;r 



detrital rocks, but in all such cases the chemically precipitated 

 silica is evidently present— though not always as distinct homo- 

 geneous bands. It is then apt to be disseminated as a binding 

 material amongst the fragmental sediments, forming horn slates, 

 fine graywackes, chert, and different very siliceous fine Bchists. We 

 have then here two forms of jaspilyte, viz: that which is inter 

 fied with green schist conformably, and that which is in masses non- 

 conformable with the green schist, or with the greenstone of the 

 region. 



There is a third sort, and this third sort is usually found in 

 immediate contiguity with the other sorts. It should, first. here 

 be stated that the Archean is divided into two main parts, the 

 Lower Keewatin and the Upper Keewatin, and that a great con- 

 glomerate is at the base of the Upper Keewatin. This great con- 

 glomerate is composed of debris, both coarse and fine, derived from 

 the Lower Keewatin. The jaspilytes already described are in the 

 Lower Keewatin, but the third sort is in the Upper Keewatin, and is 

 found in connection with this great basal conglomerate. Indeed, 

 it is simply a debris derived from the other two sorts, and it is strati- 

 fied as fragmental sediment in the midst of other sediments, evidently 

 in the waters of a widespread ocean. It is not pure and clean. It 

 does not form bands of the kind seen in the Lower Keewatin, but 

 its pieces mingle in sedimentary strata with other pieces so as to 

 make grits, graywackes and quartzytes, and to grade in fineness so 

 as to be integral parts of some schists and slates. Considering only 

 the quartz, each individual unit of the sediment is not a simple quartz 

 grain but a grain of jaspilyte consisting perhaps of many microscopic 

 quartzes. While the other two sorts may be called primary jaspil- 

 yte, this sort is certainly a secondary jaspilyte. This secondary 

 jaspilyte is seen in this view. 



(11) Secondary jaspilyte. It so happens that at the place 

 where this photograph was taken the rock has been pressed and 

 sheared so that all the parts are elongated in the same direction. 

 On the south slope of the west range of the two jaspilyte ridges at 

 Tower this secondary form of jaspilyte is seen well exposed all 

 along the southern side of the hill; and some of the detached 

 masses are very iarge. They form a part of the great conglom- 

 erate which constitutes the base of the Upper Keewatin. 



5. The rocks of the Vermilion range. 



After this particular description of the jaspilyte of the Vermilion 

 range, it is necessary only to glance at the rocks themselves tnat 

 constitute the formation in which the ore is embraced. 



FIRST, and most conspicuous and important is a great basic 

 greenstone, which shows all the characters of an old Igneous rock. 

 It is not a debris. It is not stratified, but massive. it extends 

 northeasterly to near Gunflint lake, where it seems to sin!. 

 and granite takes its place. It forms the highest hills of the 

 Giant's range of mountains, son lake. 



SECONDLY, there is a large amount of stratified green seliist. 



