158 THE CRYSTAL FALLS IRON BEAUIXG LUSTRICT. 



FOLDIIS^G. 



The extreme northwestern part of the area has not l^een studied in- 

 such detail as to enable the minor folds to be determined. In general, the 

 series may be said to fold around the Lower Huronian, followin<)- the 

 general outline indicated by its color, as shown on PI. Ill, and having- a 

 steep dip away from it. In sec. 20, T. 45 N., R 33 W., large outcrops of 

 chert are folded in a most complicated fashion and are locally brecciated. 

 South from this itoint the evidence of subordinate cross folds is marked. 

 As a result, the line between the Lower Huronian and Upper Huronian is 

 undulatory. The indentations in the Lower Huronian reiiresent minor 

 cross synclines, and the protuberances represent minor cross anticlines. 



CRYSTAL FALLS SYNCLINE. 



Near Crystal Falls is the most important of these sj-nclines. This 

 town and a number of small outlj^ing mining villages are situated on a 

 svncline. The character of this syncline is shown better by the distri- 

 bution of the Hemlock volcanics than by the sedimentaries, owing to the 

 scarcity of the outcrops of tlie latter (Pis. XVII and XVIII). The broad 

 belt of northwest-southeast trending volcanics, situated 3 miles northeast of 

 Crystal Falls, bends in sees. 11, 12, and 13, T. 43 N., R 32 W., to the 

 south, and gradually changes to a slight southwest trend. In the reentrant 

 angle of this volcanic formation is the Crystal Falls syncline, its course 

 Ijeing that of a southwestward-opening U. The axial line of this U probably 

 has a westward pitch, corresponding with the general folding of this part of 

 the district. 



Near the center of the U and just a little northwest of Crystal Falls, 

 in sees. 17 and 20, T. 43 N., R. 32 W., is an rtrea imderlain by volcanics, 

 A\diich trends east and west, and can be followed westward into sec. 1, T. 

 43, R. 35, beyond the limits of the area represented on the map. It varies 

 in width from one-fourth mile to 4 miles, averaging about 2 miles. The 

 contacts of these volcanics with the overlying Uj^per Huronian sediments 

 are not exposed. Hence definite proofs of tlieir interrelations can not be 

 given. The volcanics have been folded with the sediments, and subsequent 

 erosion has exposed them along the axis of an anticline. 



The southern arm of the curved syncline bends around the extreme 

 southern projection of the Hemlock volcanics in sees. 1 and 2, T. 42 N., R 



