Iron Ore Ranges of Minnesota. 40 



of the schist nonconformable with the schists in a manner already 

 illustrated. Several others are illustrated by Dr. Wadsworth at 

 Marquette. (Notes on the Geology of the Iron and Copper Dis- 

 tricts of Lake Superior. Mus, Comp. Zool., Geol. Ser., Vol. 1, 1880.) 



What is Jaspilyte? 



Now let us go a little more into detail. 



Anyone who has read the descriptions published in the Minne- 

 sota reports can not have failed to encounter the word "jaspilyte" a 

 great many times. it will be well to dwell a few minutes on the 

 question, What is jaspilyte? The view here seen, No. 10. 



(10) Shows a characteristic exposure of this rock. It is the 

 rock which first attracted the attention of the early explorers who 

 were seeking iron ore. It forms the summits of the great ridges 

 seen at Soudan and elsewhere. It is not always iron ore, but it 

 contains in nearly all cases a considerable proportion of hematite 

 ore. Indeed it becomes the iron ore of the Vermilion range by an 

 increase in the percentage of hematite. The beautiful banding seen 

 is formed by alternations of iron ore and silica. These bands are 

 about an inch in width, but sometimes less than half an inch, or 

 more than six inches. The silica is usually colored red, or purple, 

 or almost black, with the presence of iron, or at least of iron ore, but 

 sometimes is white. These alternating brightly colored bands form 

 a handsome surface, and their beauty is very often enhanced by the 

 manner in which they are bent and apparently twisted together. 



As there are three conditions in which this jaspilyte is found in 

 these knobs I wish to call your attention to a feature seen in this 

 slide. Along the lower side you see a change in the direction 

 and regularity of the bands. There is also a change in their com- 

 position. Some of the bands here consist of green chloritic mate- 

 rial, and as this increases in receding from the main jaspilyte mass, 

 so it grades into a green schist, and this schist is not easily distin- 

 guished from the green schist which, all about here, plays a great 

 part in the composition of the country rock. This stratigraphic 

 graduation from the alternating bands of jaspilyte into the green 

 schist cannot always be seen at the contacts of the contorted jaspilyte 

 upon the schist. But as it occurs in several places plainly, it shows 

 identity of age and method of formation — at least for those parts 

 that are thus interstratified. But care must be taken here to not 

 include the entire jaspilyte mass in this inference, for it is just as 

 plain that, even in the majority of cases the jaspilyte and the green 

 schist had different origins although about cotemporary. The con- 

 torted bands of jaspilyte have frequently an abrupt and noncon- 

 formable contact on the green schist, or on the green stone in 

 which it lies. This nonconformity is less evident in this view, but 

 can be observed at the plane where the contortions cease and where 

 the green element in the stratification begins to appear.* The only 

 inference to be drawn from this is: that from some primary source, 

 and from a greenstone as a source, contemporaneously two sorts of 

 sediment were brought into the ocean and laid out in successive 

 strata, according to the action of the ocean's currents. It can be 

 shown satisfactorily that the silica of the jaspilyte in its primary 

 masses was derived from chemical deposition and as the silica in 

 these interstratified bands cannot be distinguished from that in the 

 primary mass, it is necessary to allow that the silica In the inter 



* On the plate this plane is indicated by the two White stars. 



