66 Minnesota Academy of Science 



13. Greensand or Greenalite. 



When this green substance was first discovered it was thought 

 to be the source of the iron ore, and was called glauconite, but 

 when it was found to differ from glauconite a new name was given 

 to it, viz: greenalite, although still believed to be the source of the 

 iron ore. This green substance is not abundant, but in reality is 

 quite insignificant in amount. The actual relation of this substance 

 to the iron ore can be seen only when examined microscopically. It 

 would be too long a story, and unadapted to this audience, to detail 

 the method of this examination. Suffice it to say that this green 

 substance has nothing to do with the origination of the ore It is 

 itself a secondary product, coordinate and parallel in its history 

 with the iron ore itself, and with the limestone and the quartz. Its 

 intimate relations with the iron ore and quartz, showing its inde- 

 pendent course of development from some other source, can be 

 traced out beautifully in microscopic thin section. 



(23) I call your attention to this view. It shows the aspect 

 of the Mesabi iron ore grains, as they appear in thin section under 

 the microscope. The most of this slide is secondary quartz. The 

 round grains composed of several shells one within another are part- 

 ly made up of ore and quartz, and partly of the green substance 

 mentioned. These substances are independent of each other. They 

 do not blend, and rarely mix. They are like separate layers of 

 separate minerals in a geode. No one of them can be said to be 

 the source of the others, but it is evident that they had a common 

 source outside and entirely separate from the geode itself. 



Chemically it has been found that all the elements of the Me- 

 sabi rocks, both iron ore and quartz, as well as the green sand, and 

 the limestone and the kaolin, can be derived from the volcanic sand 

 of which those rocks almost wholly consist. It is reasonable to 

 suppose, from all the facts, that a series of active volcanoes exist- 

 ed about where the Mesabi range now is known and that their pro- 

 ducts fell into a heated ocean, whose waters attacked the debris, 

 dissolving the uncrystalline glass and distributing the results of 

 such solution in favorable places, here forming beds of quartz, here 

 of kaolin, here limestone and here of iron ore. 



(24) Another microscopic thin section shows the prevalent man- 

 ner of disintegration of the volcanic sand. As in the last the most 

 of this slide consists of quartz. It is invisible in the slide, but 

 some disintegrated grains of volcanic glass sand still show their 

 outlines, though composed mainly of iron ore. The chief purpose of 

 this view is to show the crystals of calcite which here are tightly 

 embraced in the quartz, and which must have originated at the 

 same time as the quartz, and doubtless from the same source. Such 

 •calcite, when abundant enough, forms the thin beds of limestone 

 which are found near the bottom of the black slate of the Mesabi 

 range. 



14. The Cuyuna Range. 



But you may by this time impatiently ask: What about the 

 •Cuyuna range? That is a very live subject to Aitkin. Is it entirely 

 isolated from both the Vermilion range and the Mesabi range, or 

 is it an extension from one or the other? Is its ore like that of 

 the Vermilion or like the Mesabi ore? It is evident that it is nec- 

 essary to be able to answer such questions before any intelligent 



