MINERALOGY AND PETROLOGY. 993 



Anomalous microscopic facts.] 

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who states that the volcanic fragmentals are interbedded with the iron-bearing rocks. 

 Of- this region there has been a careful study of the structural relations. Clastic and 

 non-clastic sediments are mingled with distinctly igneous materials which are some- 

 times in the form of lava flows and sometimes as "greenstone conglomerates," and 

 sometimes non-conglomeratic. This volcanic material is sometimes embraced in a 

 matrix of non-fragmental quartz, which is taken as evidence that the rock was 

 formed under water. 



7. The supposed glauconitic greensand is anomalous in containing little or no 

 potash (Bulletin x. Minnesota Survey, page 242) and in approaching in composition 

 that of a highly ferruginous basic obsidian. 



8. Very much of the iron-bearing rock, especially the low-grade ores, is not 

 taconitic (Nos. 1688, 1692), but irregularly stratified and amorphous (No. 1 under 

 No. 2 above). Yet it exhibits the same kind of transitions from rock to ore as those 

 parts which are distinctly globular in the characteristic taconitic manner. Mr. Spurr 

 has collected some of these non-taconitic rocks, viz.: Nos. 128S, 148S, 149S, 204S, 

 210S. They are represented by various numbers in the series of all the geologists. 

 Indeed, by far the greater amount of the iron-bearing rocks of the Animikie consists 

 of this gray, non-taconitic, siliceous, non-productive rock. Besides this prevalent 

 rock, the jaspilyte which is banded like that of the Vermilion range is non-taconitic. 

 This is distributed from one end of the Mesabi range to the other, but occurs nowhere 

 in so large amounts as in the Vermilion range. The question arises as to the origin 

 of this rock, for the glauconitic source can apply as a whole only to the taconitic 

 part of the series. 



Anoiitdlot/x in.icfnf<i'i>ijic furtx. 1. One of the most interesting microscopic facts 

 is the obvious and abundant origination of minerals, such as actinolite and epidote, 

 containing important amounts of magnesia and of lime, from a supposed glauconite 

 containing very small percentages of these bases, coupled with the non-occurrence 

 of any alkali-bearing minerals, although a normal glauconite contains from two to 

 seven per cent of potash (Bulletin x, page 227). 



2. On the theory that the ore is derived wholly from glauconite, or from any 

 substance undergoing metasomatosis, it is singular that in the resultant rock there 

 should be not only more iron, taken in the aggregate, than there was in the total of 

 the glauconite, but vastly more of quartz as well. This remark can be appreciated 

 fully only by one who is acquainted with the field appearances. If the widest allow- 

 ance be made for an imagined transference of these substances from one place in 

 the rock to another, the concentration of quartz in one place and of iron oxide in 

 another, the transfer still falls far short of accounting for the supposed result. The 

 formation is now, practically, totally pure iron oxide or pure quartz. Had it 



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