172 THE VERMILION IRON-BEARING DISTRICT. 



of the unaltered greenstones. In some places the vesicles are half an 

 inch in diameter, and their character is undoubted. Most commonly these 

 are filled, and the amygdules are very prominent, though in other cases 

 the amygdules have been weathered oiit. Not infrequently faint lines 

 of somewhat lighter color than the main mass of the rock may be observed 

 crossing the exposures diagonally to the schistosity. These lines seem to 

 be most common where the amygdaloidal structure is most noticeable, and 

 they appear to be the traces of flow structure in the lavas. 



In the southeast quarter of sec. 16, T. 64 N., R. 9 W., just north- 

 west of the southwestern end of Newfound Lake, there is a high hill, 

 bare over a great portion of its surface, consisting of the Ely greenstone 

 cut through and through by the granite of Basswood Lake. In some places 

 the two rocks are present in a-bout equal amount, though in general the 

 greenstone predominates. The greenstone has been so much metamorphosed 

 by the granite that it would be more accurately classed as an amphibole- 

 schist. In many places the structural peculiarities of the Ely greenstone 

 may be observed. This hill affords a good opportunity for stud}^ of the 

 relations between the granite and the schist, and especially for observing 

 the general characters of the amphibole-schists. Moreover, the fact, already 

 stated, that the greenstone does not consist of a single rock, but of a com- 

 plex, is clearly shown by the presence of a coarse, nmch metamorphosed 

 dike of dolerite which cuts the schist and includes it and which in turn is 

 cut by the younger granite. 



SECTION III— SOUDAN FORMATION. 



The Soudan formation, a division of the Archean, lies above and is 

 mainly younger than the Ely greenstone. It contains the important iron- 

 ore deposits of the district and is well developed and exposed at the town 

 of Soudan, where are located also some of the most important mines of 

 the district. 



OCCURRENCE AND CHARACTER. 



DISTRIBUTION. 



The iron-bearing formation begins 1 miles east of the western limit of 

 the distiict as outlined in this report, and can be traced eastward for many 

 miles, the easternmost occiirrence seen being a very limited exposure south 

 of Moose Lake, in sec. 4, T. 63 N., R 9 W. However, the same formation 



