326 X. H. WIXCHELL ORIGIX OP^ LAKE SUPERIOR IRON ORES 



fore, in the opinion of the authors, to find some other source for this 

 aTeen silicate of iron more immediate and more ready to furnish it. 

 They reach the conclusion that the source of this green silicate of iron 

 as well as the iron carhonate must have l)een some 1)asic igneous rock. 

 Basic igneous rock is specifically excluded from the cotemporarv Animi- 

 kie, although it is admitted that it "mav really not he so distant as now 

 appears" (page 50T), and some consideration is given as to the cause of 

 such exemption. But in the Keewatin the association of the iron-l)eariiig 

 rock with basaltic intrusion and extrusion is dwelt on at some length : 

 this basic rock's agency, however, was its effect on the cotem[)()rary sedi- 

 mentation. It is not recogTiized in any case as the early bodily repre- 

 sentative of any of the present iron masses. 



In this result, so laboriously wrought out, the authors confirm, as far 

 as they go, the conclusion of the writer in 1900. They would have ren- 

 dered a greater service to geology, and would have confirmed every con- 

 tention of the w^riter in 1900, if they had gone a step or two further and 

 clearly designated in the case of the Animikie the igneous rock to which 

 they appealed. The writer has shown, as already stated, that the bulk 

 of the Mesabi formation consists of lava and fragmental oljsidian. Xear 

 the bottom this igneous matter, especially that which is uncrystallized, 

 was disintegrated in situ into its chemical elements, and these elements, 

 where insoluble or difficultly soluble, have constituted the masses of iron, 

 quartz, kaolin, and limestone which are f(nind. 



Some confusion and contrariety of opinion have resulted from a fail- 

 ure to study carefully the jaspilyte. It has been observed that the band- 

 ing is bent in so close folding that it is impossible to imagine that the 

 formation in which it lies has been so folded, and yet it is difficult to 

 understand how the iron ore and jasper could have been so folded with- 

 out an identical folding of the associated greenstone. On the other hand? 

 it has been observed that sometimes, and even in immediate connection 

 witli the folded jaspilyte, there are plainly sedimentary bands of jaspilyte 

 alternating with thin strata of other kinds of sediment, the latter usually 

 being green, but sometimes of chemical silica or of hematite. This 

 sedimentary origin ])eing so evident, a hasty ins])ection has usually led 

 to the idea of sedimentary origin of all the jaspilyte. The error has been 

 in that assumption. J. D. Whitney only distinguished the two. It will 

 be observed that where the contorted jaspilyte lies nonconformable in 

 the midst of the greenstone, in nearly all cases there is on one side or the 

 other (which may be taken as the ypper side in the order of formation) 

 a belt of greater or less width composed of strictly parallel strata made 

 up largely of jaspilyte of identical composition, but interstratified with 



