y56 THE VERMILION IRON-BEARING DISTRICT. 



deutly than the rocks with a smaller amount of the miciocline. This is 

 evidence in favor of the microcline twinning having been produced by 

 pressure. The quartz and feldspar occasionally are in micropegmatitic 

 intergrowths. Some secondary minerals occur with these rocks, such as 

 chlorite, sericite, and epidote. 



RELATIONS TO ADJACENT FORMATIONS. 



The Giants Range granite is found at different places in juxtaposition 

 with the Ely greenstone, the Soudan formation, the Lower Huronian sedi- 

 ments, and the Keweenawan gabbro, enumerated in order from the base up. 

 Its relations to these formations are in each case quite clearly shown and 

 will be specifically described in the following paragraphs. 



Relations to the Ely greenstone. — The granite cuts the greenstones con- 

 stituting this formation in innumerable dikes which individually seem to 

 have little effect upon the greenstone, judging from the lack of well-marked 

 contact zones adjacent to the dikes. As we get nearer the contact between 

 the greenstone and the granite massive, however, exactly the same kind of 

 metamorphic products are observed as are found associated with the contact 

 of the intrusive granite of Trout, Burntside, and Basswood lakes with the 

 Ely greenstone on the northern side of the district. As the dikes increase 

 in number the greenstones are altered to amphibolitic and micaceous schists, 

 frequently still retaining the unmistakable amygdules and ellipsoidal parting 

 of the original greenstones. Similar products of the granite intrusion have 

 been described under the description of the effect of the granite of Trout, 

 Burntside, and Basswood lakes on the Ely greenstone (p. 166 et seq.). 



Relations to the Soudan formation. — The Soudan formation is, as has been 

 stated, of very limited extent, and consequently there are few opportunities 

 for observing granite dikes in it. However, such dikes have been observed 

 at a number of places (see p. 359), and their presence shows clearly that 

 the Giants Range granite cuts the Soudan formation and is hence younger 

 than it. 



Relations to the Lower Huronian sediments. — The Duluth and Iron 

 Range Railroad, south of Tower, especially in the vicinity of milepost 92, 

 gives very good sections through the Lower Huronian sediments and sliows 

 them to be cut by dikes of granite. These dikes vary in size on different 

 exposures, ranging from 1 inch up to 4 feet in width. They can not be 



