CONCLUSIONS OF AUTHOR AND OTHER WRITERS DIFFER. 320 



one place varying within a foot or two as much a.s 4.">° or 50° ") seemed 

 to me to indicate the irregular outline of an eruptive mass rather than 

 the sinuous outcrop resulting from prior erosion. On the other island, 

 only a very short distance away, there is an apparent transition from 

 the granite to the conglomerate. The conglomerate is very massive, so 

 that the strike and dip could not he ascertained with any degree of cer- 

 tainty, and near the line of contact shows abundant signs of alteration. 

 The contact between this granitic mass and the Huronian was also ex- 

 amined by the late Mr Alexander Murray at the southeastern end of 

 Lake Pakowagaming. On a manuscript ma}) to which I lately had 

 access Mr Murray states that near the junction the Huronian is com- 

 posed of a red-colored altered quartzite, slate and conglomerate, dipping 

 north or away from the granitic mass at an angle of 80°. To the south 

 and in immediate juxtaposition with the granitoid gneiss "the slates are 

 corrugated and contain patches of red feldspar." A little to the north- 

 west "'the wrinkled and contorted quartzite and slate are cut by granite 

 veins, mica and epidote." The rocks on the southwest side of this lake 

 have all a high inclination northward, while on the northeast side the 

 slates and quartzite are nearly if not quite flat. 



Dr Selwyn lias frequently pointed out, both in personal conversation 

 and elsewhere, that the Hnronian must be regarded as preeminently a 

 pyroclastic series of rocks, and if this fact is borne in mind the occur- 

 rence of most of the so-called conglomerates will he more susceptible of 

 explanation. These occur at various horizons through the series, and 

 very frequently intimately associated with the massive diabases. They 

 seldom, if ever, contain pebbles of gneiss, and the most abundant frag- 

 ments seem to be of coarse red or gray syenitic granite. As agglomerates 

 or breccias, some of whose fragments have become rounded by the action 

 of water, they neither represent a want of conformity nor a great lapse 

 of time, and simply occur as additional proofs of the intense volcanic 

 activity which must have characterized this epoch. 



The line of demarkation is very seldom a simple plane of division, the 

 breccia present along the junction frequently covering a considerable 

 space. It is therefore often impossible to draw an accurate line of divis- 

 ion between these two rocks unless we assume that such a line should 

 he placed where the two rocks are present in about equal proportion. 

 The general correspondence of the gneissic intrusions with the stratifica- 

 tion of the enclosing schists and the frequent lenticular outline and par- 

 allel disposition of the detached schistose fragments in the gneiss often 

 resemble at first sight an alternating sequence of transitional beds. 

 Again, the crystalline condition of the Huronian feldspathic and mica- 



XLIX— Bum.. Geot,. Soc. Am., Vol. 4, 1892. 



