332 N. PI. WINCHELL SAPONITE, THALITE, GREENALITE, GREENSTONE 



beds of iron oxide, and perliaps of iron carbonate, of silica, kaolin, and 

 occasional^ of marble. 



Tlie idea that tliese hydrous silicates of iron and magnesia or any of 

 them may be formed by chemical sedimentation from the oceanic waters 

 is apparently unnecessary and impossible. If it were proven that they 

 are soluble at oceanic temperatures the question arises, Why would they 

 not be carried away by the currents of the ocean along with the soda and 

 most of the lime? Also, Why do they now have fragmental and, as on 

 tlie Mesabi range, globular forms? Also, Why are they not found in 

 distinct sedimentary sheets like marble and kaolin? And why do the 

 associated chemical products, such as iron oxide and silica, present the 

 same globular shape? It may be admitted that from an alkaline ocean 

 there may have been chemical deposition of silica and iron oxide under 

 certain conditions, but it is hard to understand why such deposit should 

 in any case take the shapes which they and the greenalite exhibit on the 

 Mesabi range. Since the iron ore and the silica, having the same origin 

 and date, assumed identically the same shapes — that is, forms of detrital 

 grains — it seems much more probable that a common cause controlled 

 them all. There appears to be no possible hypothesis that will answer 

 all the conditions but to assume that they took the shapes of preexisting 

 detrital grains, and it follows from this that those grains were of such 

 a nature that these secondary substances could be injected into them or 

 produced by them. No detrital substance in the form of sand is known 

 which is so easily altered as volcanic glass, or basaltic sand ; and, in the 

 light of the foregoing, it seems warrantable to infer that the original 

 grains which gave shape to the greenalite and to the iron ore and to the 

 rounded secondary quartz grains were grains of volcanic sand. Further, 

 this hypothesis will not exclude the same alteration of adjacent sheets of 

 lava and more or less crystallized trap, cotemporary witli the produc- 

 tion of these minerals in the volcanic sand ; and in the case of consider- 

 able quantities of obsidian, which was not broken and distributed as 

 sand, such masses would have been liable to the same change, namely, 

 they would be likely to lose all their natural ingredients, maintaining 

 their shape and their fluidal structure, and would present the banded 

 structure seen in jaspilyte. Sucli masses are found not only on tlie 

 Mesabi range, but in the ore bodies of the Vermilion and Cuyuna ranges. 



