466 E. L. BRUCE 



river flood plains. This group, the lower and upper Missi forma- 

 tions, are, however, on structural evidence, thought to be sepa- 

 rated by a mountain-making and erosional interval from the 

 volcanic rocks and are therefore not considered in this discussion 

 of the early pre-Cambrian formations. 



In the Wekusko (Herb) Lake district, approximately seventy- 

 five miles east of the Saskatchewan-Manitoba boundary, elHp- 

 soidal lavas occur which are apparently the continuation, so 

 far as lavas can be continuous, of the area just described. They 

 are Hthologically similar and outcrop practically continuously 

 across the interval. Quartz-biotite gneisses Hthologically similar 

 to the Kisseynew gneiss are associated with them. StauroHte 

 schist, conglomerate, slate, and acid volcanic flows also occur. 

 AU these are interbanded with the basic elKpsoidal flows. 



Alcock's summary"" is very definite with regard to the relations 

 and character of these early rocks: 



The pre-granite complex is interpreted, therefore, as representing a 

 series of interbanded sediments and volcanic rocks of varying composition. 

 Though the sedimentary division contains members which have pebbles of 

 granite, quartz, and volcanic rocks, no evidence was found that these pebbles 

 were derived from any rocks now exposed in the area, nor was any evidence 

 found, aside from the presence of these bowlders and pebbles, which would 

 suggest that the members containing these fragments represent a younger 

 series infolded with the complex and separated from it by an erosional uncon- 

 formity. The whole group is regarded as a series of flows and contemporaneous 

 sediments. The absence of limestone, the dominance of clastic sediments, 

 the irregularity of the beds, the great thicknesses locaUy, the recurrence of 

 conglomeratic horizons, point to a continental rather than to a marine origin 

 for the series.^ 



At Cross Lake, an expansion of the N,elson River below Lake 

 Winnipeg, a series of sedimentary rocks consists of para-gneiss, 

 arkose, and conglomerate; some of the gneisses are garnetiferous. 

 Greenstone, which in places is ellipsoidal, occurs in the area. The 

 sediments are interbanded with the lavas. They are interpreted 

 as continental, probably fluviatile deposits.^ 



' F. J. Alcock, Memoir iig, Geol. Survey of Canada. 



^ Ibid., p. 24. 



3 F. J. Alcock, Summary Report, Geol. Survey of Canada, Part D (1919). 



