816 THE GEOLOGY OP MINNESOTA. 



[Granite. 



No. 1987. GRANITE. 



Same place as the last. 



Ref. Annual Report, xxiv, page 1. 



Meg. A later granite dike, cutting No. 1986. 



Mic. This rock is like the last, but having less contrast as to size between the 

 old and the fresh feldspars, the latter also being more numerous as compared with 

 the interstitial new growths, and thus coming occasionally into contact; but such 

 contacts are characterized, as in No. 1986, by the same appearance of apposition 

 rather than crystalline intergrowth, except that usually a fresh deposition of clear 

 glassy feldspar or of quartz cements them by a continuous line or by several nearly 

 adjacent grains. Quartz also enters the old feldspars as a vermicular micro- 

 pegmatyte. One section. 



Age. Archean dike. 



Remark. There is no way of knowing whether much or little time separated 

 the dates of formation of these dikes. They are petrographically so similar that 

 they seem to have had nearly the same date and the same origin. N. H. w. 



No. 1990. GRANITE. 



Menan island, near the last. 



Ref. Annual Report, xxiv, page 1. 



Metj. This is a light-gray, rather fine-grained dike six inches wide, showing 

 contact on schist, apparently the youngest of the dikes. 



Mic. The larger old feldspars are quite scarce in this rock, but very many of 

 the grains in the finer matrix are surrounded by a rim of secondary growth which 

 interlocks with rims that likewise surround adjacent grains, the centres of the 

 grains being crowded with mica scales and sometimes containing secondary silica. 

 Epidote is quite common, and is lodged within the old feldspars, or in the finer 

 groundmass. Green hornblende also forms a conspicuous part of the slide, being later 

 than the few biotite scales which it encloses. One section. 



Age. Archean dike. N. H. w. 



No. 1991. GRANITE. 



N. W. J4 S. E J^ sec. 26, T. 63-17, northern part of Vermilion lake, where the canoe route turns north on 

 the east side of the channel. 



Ref. Annual Report, xxiv, page 1. 



Meg. Resembling outwardly the rock No. 1990, this forms a laccolith or 

 spreading mass in the midst of the schists and granites, constituting the highest part 

 of a knob a little back from the lake, supposed to be of the same origin and age as 

 No. 1990. 



Mic. This rock shows well the contrast between the old feldspars and the new. 

 The old form cores which are surrounded by fresh rims, as already mentioned, and 



