THE LOWER HURONIAN. ' 353 



dikes penetrate the surrounding Lower Huronian sediments and other adja- 

 cent rocks. The large masses especially have produced on the adjacent 

 rocks far-reciching metamorphism. In addition to these main areas and 

 the dikes which can be connected with them, there are throughout the 

 district acid dikes which vary somewhat in peti'ographic characters and 

 which penetrate the various formations adjacent to them. The largest 

 masses of these acid rocks occur in the core of the Griants range, in the 

 vicinity of White Iron Lake, extending northeast and southwest of that 

 area, and in the vicinity of Snowbank and Cacaquabic lakes, and are 

 described below. In addition, a section will be devoted to a brief description 

 of the various dikes which can not properly be connected with these 

 masses, but are assumed to be of essentially the same age. Still another 

 section is given to a very brief description of certain basic and intermediate 

 dikes which have been found to bear the same relations to the adjacent 

 formations as the acid intrusives bear, and which are hence presumed to be 

 of the same age. 



GIANTS RANGE GRANITE. 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



Distribution. — The Giants Range granite borders a portion of the south- 

 ern side of the Vermilion district, and is best developed in that part of the 

 area extending from the vicinity of Beaver River, in sees. 31 and 32, T. 62 N., 

 R 13 W., eastward into sees. 24 and 25, T. 63 N., R. 10 W. Immediately in 

 the vicinity of White Iron Lake it reaches a very extensive development, 

 and to the southwest, in the portion of the Giants range in the Mesabi 

 district, it occupies the core of the range, and here shows its typical 

 characters, and has therefore been called tlie Giants Range granite. The 

 granite underlies a A^ery much greater area than is shown on the map 

 (PL II). According to the Minnesota maps, and also as observed in a 

 reconnaissance trip, it extends a number of miles to the south of the area 

 here described, where it is bordered by the Duluth gabbro mass. This 

 gabbro mass likewise cuts across it in the northeast-southwest direction, 

 gradually nearing the area underlain by the granite as it is followed east- 

 ward, until in sec. 19, T. 63 N., R. 9 AV., the granite is completely cut out 

 by the gabbro. The area underlain by this granite thus varies from a 

 very narrow strip on the east, where it actually feathers out, to an area 5 

 MON XLV — 03 23 



