, S. GEOLOGICAL SURVEV 



MONOGRAPH ) 



Formation name. 



Colum- 

 nar SEC- 

 TION. 



Character cf rocks. 



I , I I 



Randvills dolomite. 



^ 



Thickness unknown Yellowish to reddish brown sandstone, not 

 thortiughly cemented, therefore disintegrates readily. Found in patches 

 in many places, and always lying either in beds wh=ch are horizontal or 

 else possess slight dip to the south This may represent the initial dip 

 with which the beds were deposited. 



A series of very great bui unknown thickness. It consists of alte 

 ing beds of slates, graywackes, siderite. and chert. With these, f 

 cially associated wilh ihe last two, are found hematite and limonit 

 bodies of variable size and of great economic importance. Fronr 

 series is derivpd nearly all the ore supplied by the Crystal trails dis 

 In the southern part of the district, especally well exposed ir 

 vicinity of the Paint and Michigamme rivers, the slates and graywa 

 have been metamorphosed into schists and gneisses, This series i 

 by dikes of rock ranging from acid to ^jltrabasic. which have, in pli 

 metamorphosed ihe sediments. 



The thickness of this vast pile o- volcanic ejectamenta can not be 

 estimated with any degree of accuracy. It consists chiefly of interbed- 

 ded acid and basic lavas and associated tuff deposits, and the water- 

 deposited ma*en'ls derived from them. Near the top of the volcanics 

 a lent.cular aiea of norma' sediments, slates with lenses of limestone, is 

 found. This forn-,ation is cut by acid and basic dikes. 



Estimated to be about 1 .SOOfeetthic 

 lentals, slates, and graywackes and.assc 

 nd carbonate F rom these last has be 

 /ilh them The Mansfield mine, by v^ 



;, It consists of interbeddedfrag- 

 :iated with these. feriuginouschert 

 n derived the ore found associated 

 xploited the only ore body 



s theonly Bessemerore of the Crystal 

 metamorphosed by basic dikes. 



The thickness is that estimated for this formation in the eastern part 

 of the district by Smyth. The prevailing rock is quartzose dolomite 

 a very friable character. 



it shows the usual characters of granite 

 nassif, and is cut by acid and basic d\[ 



chistose on flanks of 



GENERALIZED COLUMNAR SECTION. 



