THE IRON SERIES, CONTINUED. 



105 



them, like intruded dikes. Wadsworth mentions Dr. Selwyn of 

 the Canadian Survey, and the late C. E. Wright, as supporters of 

 this view. While it may not as yet be possible to demonstrate 

 beyond question the true origin, it is quite inconceivable that 



FIG. 18. Cross sections to illustrate the occurrence and associations of 



iron ore in the Marquette district, Michigan. After C. R. Van Hixe, 



Amer. Jour. Sci., February, 1892; Engineering and Mining 



Journal, July 9, 1892. 



a nearly pure siliceous rock and an equally pure basic oxide should 

 be side by side and intimately associated as intrusive masses. They 

 would combine. Quite large masses of iron oxide may and do oc- 

 cur as segregations of basic magmas ; not, however, in any amount 

 in acidic. All other geologists who have given the matter atten- 

 tion concur in some form of sedimentary origin, or in origin by re- 



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