1 86 H. C. COOKE 



on Kaopatina Lake where most of the outcrops are hidden by a 

 heavy cover of drift. The plunge of the folding appears to have 

 been to the east, for near the west end of the area the strikes assume 

 more of a north-south trend, which may indicate the presence of 

 the axis of a cross-fold near-by, though it may be due merely to the 

 subsequent disturbing influence of the granite intrusion to the west. 



The basal rocks of the series, found on the river above Bras 

 Coupe Lake, are very basic basalts, one flow of which is unusually 

 fresh and glassy. These, like the basal flows on Father's Lake, 

 possess no ellipsoidal structures. They are overlain to the south, 

 as far as the outlet of Windy Lake, by andesites characterized by 

 good pillow structures. A thin body of somewhat more acid lava 

 lies above the andesites, and on this is found a bed of coarsely frag- 

 mental rhyolite, approximately 2,000 feet thick. Its composition 

 is identical with that of the massive rhyolite porphyry on Opawika 

 Lake. This fragmental rock shows no trace of bedding, as would 

 a water-laid sediment, although we may conclude from the evidence 

 of the pillow structure in the underlying andesites that the sea or 

 a lake existed here at the time. It seems necessary to conclude 

 therefore that the rock was not ejected as a tuff, but as a lava, and 

 that its present fragmental condition is due to subaqueous extru- 

 sion, and hence corresponds to the pillow structure in the more basic 

 lavas. Corroborative of this conclusion, rhyolite porphyry in the 

 same fragmental condition was also found on Obatogamau Lake, 

 where it rests directly on well-bedded tuffs, thus again indicating 

 its subaqueous extrusion. 



The southern boundary of the fragmental rhyolite is a fault, to 

 the south of which the ellipsoidal andesites again outcrop. 



Between the south shore of Windy Lake and the south shore of 

 Kaopatina Lake the structure is unknown, as outcrops are not 

 numerous or large enough for its determination, although there are 

 sufficient to indicate that the formation is continuous across the 

 gap. However, since the outcrops on the south side of Kaopatina 

 Lake are of the basalts of the series, which elsewhere always occupy 

 a basal position, and since they still maintain an east-west strike 

 and a dip to the south, the intervening drift-covered gap must be 

 supposed to be underlain by the south limb of a syncline whose 



