432 THE CRYSTAL FALLS lEON-BEARlNG DISTRICT. 



South of the Archean dome in the Michigamme Mountain area the 

 dolomite tops the low arch in a broad crumpled sheet, in the minor syn- 

 clines of which the higher formations are more and more implicated as we 

 go south. This broad sheet, with its included tongues of phyllite, extends 

 to the south line of T. 44 N., R. 31 W., beyond which it disappears beneath 

 the higher formations, except in a single narrow belt which continues along 

 the main axis for about a mile farther south. Exposures sufficient in num- 

 ber to indicate several minor folds are found along the Michigamme River 

 and scattered through sees. 28, 32, and 33, T. 44 N., R. 31 W., and sec. 4, 

 T. 43 N., R. 31 W. 



FOLDING AND THICKNESS. 



In attitude the Randville formation in the Fence River division of the 

 district is an eastward-dipping monocline, the inclination of which is gen- 

 erally moderate. The rocks are usually heavily bedded and nearly always 

 show distinct alternations in coarseness and color, so that structural obser- 

 vations are made with much more certainty than in the Felch Mountain 

 range. The more conspicuous minerals secondarily developed here — coarse 

 carbonates and tremolite — have formed chiefly in the old planes of bedding. 

 Oblique structures are generally absent except in the close vicinity of the 

 basic dikes which intersect the formation along the upper river section. 

 The surfaces of contact with the dikes stand at high angles, and nearly 

 parallel to these the neighboring dolomite has well-developed cleavages, 

 along which new minerals have formed, intersecting the true bedding. It 

 is evident that the stronger igneous rocks in these cases have furnished 

 resistant surfaces against which the dolomite has been kneaded in the 

 general tilting of the series. 



The eastward-dipping monocline is a simple one, yet the observed 

 angles of inclination are by no means uniform. Thus, along the upper river 

 section the dip ranges from 25° to 60°, with 40° as the mean of about a 

 dozen observations. The variable dips are so scattered through the cross 

 section as to indicate no widespread roll in the formation as a whole, but 

 rather a great number of minor undulations probably distributed through- 

 out its thickness. Such undulations are visible in favorable localities, as, 

 for example, on the north bank of the river in the NW. ^ of NW. ^, sec. 

 28, T. 45 N., R. 31 W., where fresh surfaces have been exposed in blasting 



