Reviews. 



The Iron-Bearing Rocks of the Mesabi Range in Minnesota. By 

 J. Edward Spurr. Bull. No. X. of the Geol. and Nat. 

 Hist. Surv. of Minn. Minneapolis, 1894, pp. 259, 10 plates 

 and figures in the text. 



While this volume presents nothing new in general results, it is an 

 interesting expansion of the summary given in the American Geologist 

 for May, 1894, and forms a valuable supplement to Bull. No. VI. on the 

 Iron Ores of Minnesota, and the Mesabi Iron Range by H. V. Win- 

 chell in the 20th An. Rep. of the Geol. and Nat. Hist. Surv. of Minn. 



Part of the bulletin is devoted to a detailed description of the strat- 

 igraphy and the megascopic and microscopic study ot the different 

 classes of rocks which serve as a basis for several chapters of more 

 general scientific interest in which such questions as the Process of 

 Metasomatosis ; Metamorphic Agents ; Prismatic Jointing ; Slaty 

 Cleavage; Banding and Bedding; the Origin of the Iron-Bearing 

 Rock ; and the Formation and Structure of Ore Deposits are dis- 

 cussed. 



Mr. Spurr makes the following classification of the iron-bearing 

 rocks : 



1. The normal class including (a) the primary spotted-granular 

 rocks, (f) the ferruginous spotted-granular rocks, (c) the siliceous 

 spotted-granular rocks. 



2. The oxidation and concentration class, including (a) the leached 

 rocks and (b) the ferrated rocks. 



3. The shearing class including (a) the magnetite-hematite slates, 

 (b) the chlorite actinolite slates, (c) the silica slates. 



4. The impregnation class. 



5. The shearing impregnation class. 



As the underlying and overlying rocks show very little metamorph- 

 ism, the writer concludes that the metamorphic agents could not have 

 been heat or mechanical disturbance, but were oxygen, alkalies, and 

 acids carried in by the surface waters. 



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