260 THE VERMILION IRON-BEARING DISTRICT. 



the unconsolidated magma. Between rocks formed in this Avay and those 

 formed as tlie result of pressure, but in which complete recrystallization has 

 taken place, no distinction can be made. In the areas examined the 

 massive granites predominate greatly over the schistose rocks. In the fol- 

 lowing brief description only the massive granites will be considered. 



Microscopic characters. — The mineral constituents are green hornblende, 

 biotite, orthoclase, quartz, and plagioclase, with accessory sphene, zircon, 

 and iron oxide. These minerals have been very much altered, so that their 

 places are taken largely by secondary minerals, of which chlorite is the 

 most prominent, and, after this, epidote and sericite and secondary feldspar, 

 There is a variation in the mineral character, hornblende being practically 

 wanting in some specimens and increasing verj^ much in quantity in others. 

 No cases were found in which the quartz was wanting, but it was reduced 

 in quantity in some cases. The Trout, Basswood, and Biirntside lakes acid 

 rocks seem to vary from hornblende- and mica-granites to syenites, with the 

 granites predominant. 



RELATIONS TO ADJACENT FORMATIONS. 



Relations to Ely greenstone. — Iii approaching that portion of the district 

 in which the granite of Trout, Burntside, and Basswood lakes is exposed we 

 cross over a broad area underlain by the Ely gi-eenstone in its typical 

 development, in which only rarely is a granite dike to be seen. The closer 

 we get to the contact between the two above-mentioned formations the more 

 numerous, however, become these granite dikes, until in places they are so 

 common that we may almost consider the greenstone as having been thor- 

 oughly permeated by the granite magma. This intimate relationship is 

 beautifully shown on the numerous exposures at the west end of Burntside 

 Lake. It should be stated in this connection that the gi-anite dikes cutting 

 through the rocks exposed on the shores of this lake do not all belong to 

 exactly the same period of intrusion, but show some slight differences in 

 age. These differences are not, however, thought to be great. In other 

 words, all of the granites are believed to belong to essentially the same 

 period of intrusion. 



From the intrusive relations above illustrated it is clear that the granite 

 is younger than the adjacent greenstone. This intrusive relation is further 

 emphasized by the progressive metamorphism shown by the Ely greenstone 



