230 A. P, COLEMAN—CLASTIC HURONIAN ROCKS. 
Of the smaller areas mention may be made of Sultana island a few 
miles from Rat Portage, famous for its gold mine. Here a boss of coarse 
porphyritic granitoid gneiss a mile in length by half a mile in width 
presents the same eruptive contact with the green Keewatin rocks as one 
finds around the larger masses. Another similar boss of coarse Lauren- 
tian granite was found by the writer at Caribou lake, east of the lower 
end of lake Manitou, the area being only about a square mile. Hxam- 
ples of intermediate sizes may be found on the Canadian Geological Sur- 
vey’s maps of the region. 
Finer grained granites, generally showing no foliation on the edges of 
the areas, are common also both in Huronian strips and in the Lauren- - 
tian; and many more small knobs and bosses than were mapped by 
Lawson in his somewhat hurried work will be found from time to time ; 
such as the area of protogine containing so many gold-bearing veins at 
Laurentian. (—} kway, CoucwicHinc. ¥ Gran/re. 
° 2s 
Scare or Mies. 
Fieure 1.—Geological Map of Part of Western Ontario. 
Shoal lake. So far as known, these granite bosses are later than both 
Keewatin and Laurentian, having penetrated both. It is, however, not 
always easy to say whether a given rock is Laurentian or a later granite, 
and it is likely that the two are connected in origin and might be ar- 
ranged as a consecutive series. Both Laurentian and other granites send 
off felsitic dikes into the adjoining rock, and in this way one may often 
discover the proximity of a gneiss or granite area'a quarter of a mile 
before reaching the contact. 
It is worthy of note, as observed by Lawson, that often the gneiss 
grows darker and more basic near the contact with basic Huronian rocks, 
as though some of the latter material had been incorporated in the un- 
derlying Laurentian. 
The accompanying map, figure 1, will illustrate the geological relation- 
ships just mentioned. It hasbeen pantographed from three map sheets 
issued by the Canadian Geological Survey—the Rainy Lake, Seine River, 
