406 THE CRYSTAL FALLS IRON-BEARIKG DISTEICT. 



SECTION V. THE RANDVILLE DOLOMITE. 



The Sturgeon quartzite is succeeded by a formation consisting, so far 

 as is known, almost wholly of crystalline dolomitic rocks. Excellent 

 exposures belonging to this formation are situated within a short distance 

 of Randville station, on the Milwaukee and Northern Railway, and it may 

 therefore conveniently be named the Randville dolomite. 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



Owing both to its great thickness and to its intermediate position in 

 the series, the Randville dolomite in the Felch Mountain range coveis a 

 larger share of the surface than any other member of the Algonkian suc- 

 cession. The overlying formations are frequently interrupted, because of 

 the changes in direction of pitch of the secondary synclines in which they 

 occur. In these gaps the dolomite covers the whole interior of the syncli- 

 norium. Wliere the higher formations are present, they divide the dolomite 

 into two or more parallel east and west belts, one of which lies south of the 

 northern quartzite and the other north of the southern. Only in portions 

 of sees. 35 and 36, T. 42 N., R. 29 W., where the rise in the axis of the 

 main syncline has lifted it above the present surface of denudation, is the 

 dolomite entirely absent from the main trough. 



Natural exposures of the dolomite are not so numerous as of the 

 quartzite, but they are more evenly distributed. Moreover, owing to its 

 proximity to the Groveland iron formation, the dolomite has been penetrated 

 by many test pits and diamond-drill borings put down in search of ore, 

 and these supply important information in the covered areas. From the 

 western end of the map to sec. 34, T. 42 N., R. 29 W., the dolomite is for 

 most of the way separated into two or more parallel belts. The southern 

 belt is especially well exposed in sees. 35 and 36, T. 42 N., R. 30 W., and 

 in sec. 31, T. 42 N., R. 29 W., and for 2 miles to the northeast, beyond 

 which it has been found only in test pits and drill holes. In the middle of 

 sec. 35, T. 42 N., R. 29 W., the base of the formation is brought to the 

 surface by the westerly pitch of the main fold and is well exposed along 

 Sturgeon River. 



North of the strike fault, which, as already described, has brought the 



