AREAS ABOUT THE INTERNATIONAL BOUNDARY. 365 



On all sides of this Area occur other and similar areas, encircled by belts of 

 crystalline schists and separated from each other, as in Minnesota, by vertical 

 synclinally folded troughs of semi-crystalline schists. The Area on the 

 south has just been mentioned as the Vermilion Area. Some of the others 

 have received from Dr. Lawson special names. The Sabaskong Area lies 

 northwest of this, separated from it by a belt of semi-crystalline schists about 

 three miles wide and stretching to the Lake of the Woods. This Area is 

 about 25 miles in diameter. Between the two areas, however, the small 

 Minomin Area, which is ten miles long and five miles broad, is crowded in- 

 Northwest of the Sabaskong Area lies the Obabikon Area, embracing the 

 whole of the Grand Presqu'ile of Lake of the Woods and Whitefish bay.* 

 It is 33 miles in greater diameter, N. 67° W., and 29 in the transverse direc- 

 tion. This Area, like the others, is girded by inclosing schists on all sides, 

 except perhaps a small break at the south. The belt of schists on the north- 

 west side attains a diameter of 20 miles. Within that breadth, however, 

 occur half a dozen exposures of granitoid rock, each encircled by schists 

 approaching a concentric strike. Beyond the bounding schistic belts are 

 other gneissoid regions stretching toward the northeast, north, and northwest 

 for distances not yet ascertained. From the Staujikoming Area toward the 

 east and northeast are other little exposed areas, while on the north is the 

 so-called Lake Harris Area. Between the Lake of the Woods and Thunder 

 bay, granitoid rocks are known to alternate several times with crystalline 

 and semi-crystalline schists, but the several areas have not been circum- 

 scribed by explorations. 



Within each of the areas thus indicated the underlying rock is predomi- 

 nantly gneissoid. It is not everywhere equally foliated. If it anywhere 

 approaches the granitoid condition that is the part more remote from the 

 periphery. Within some of the larger areas we find two or more granitoid 

 centres, and around each of these the lines of gneissic foliation are concen- 

 trically arranged. Dr. Lawson states that in the Stanjikoming Area of 

 Rainy lake the more basic gneiss occupies, within the general Area, the belt 

 next contiguous to the environing crystalline schists ; the mere acid surrounds 

 the nuclear region. The former is a syenite gneiss with little or no quartz, 

 having a coarse texture and imperfect foliation. The more nuclear portion 

 is essentially a biotite gneiss of medium texture, very quartzose and distinctly 

 foliated. 



Sporadic eruptions of granite occur, cutting sometimes the gneisses and 

 sometimes the crystalline and newer schists, but of these I have no occasion 

 to make particular mention at present. 



*For the geology of the Lake of the Woods see Lawson, Geol. and Nat. ITist. Surv. of Canada, 1885 

 Report CC. 



XLVIII— Bull. Geol. Soc. Am., Vol. 1,1889. 



