PETEOaEAPHIGAL CHAEACTEES OF EANDVILLE DOLOMITE. 435 



deep blue, and pale green. Where weathered, the usual colors are light 

 brown or buff. The lighter-colored rocks in general are characteristic of 

 the Fence River area where metamorphisni is more uniform and more 

 intense, and the darker colors of the Michiganame Mountain area to which 

 the less crystalline forms are wholly confined. Bands differently colored 

 are nearly always present in the same outcrop. 



In the Michigamme Mountain area the torsional strains attendant upon 

 the formation of folds in two directions have developed two systems of frac- 

 ture in the dolomite. In these secondary quartz has formed, occasionally 

 in large amount. Of much interest is the occuiTence in close connection 

 with such vein quartz of occasional thin bands of pegmatite, doubtless aris- 

 ing from the action of deeply derived waters. In similar spaces coarse 

 secondary carbonates, tremolite, and oxides of iron also have commonly 

 formed. Over the small anticlinal axes and domes of this area the original 

 bands of the rock have often been shattered, and are now recognizable only in 

 displaced fragments cemented together by the new minerals. In the Fence 

 River area the general secondary folding has been attended with differential 

 movements along the bedding, which left narrow open spaces where the 

 adjacent surfaces failed to fit in their final position of rest. These sjDaces are 

 now indicated by coarsely crystalline carbonates and silicates arranged nor- 

 mal to the original walls. Where the space was a wide one the outer walls 

 are iisually lined with coarse calcite, while the interior is filled with quartz. 



In the Michigamme Mountain area certain pink bands of the dolomite 

 have a beautiful oolitic texture, which is most clearly brought out in weath- 

 ering by the geometrical regularity of distribution of the harder shells or 

 cores of the little rounded grains. The forms are not different from and are 

 quite as distinct as those in the oolitic limestones of recent deposition. 



The chemical composition of the dolomites is illusti-ated by the follow- 

 ing partial analyses by Mr. R. J. Forsythe, of Harvard University : 



Analyses of dolomites from Michigamme Mountain area. 



II. 



Eesifiue iusol. in HCl 



Al2(Fe2)03 



CaC03 



MgCOs 



14.25 

 11.15 



47.18 

 18.48 



9.34 

 12.57 



45.98 

 19.23 



5.38 

 36.60 

 16.38 



