STRUCTURAL FEATURES OF THE PRE-CAM BRIAN 369 



Kemp, and Smyth describe the Grenville series and older granite- 

 gneiss as much more metamorphosed than the intrusive anorthosite, 

 a fact which may indicate an early folding, but may also be due to 

 the greater competence of the anorthosite to resist the later folding. 

 The evidence is slight, but it is very possibly the case that the 

 marginal intrusion of granite accompanying the upHf t of the Gren- 

 ville continental segment at the close of Grenville time was accom- 

 panied by marginal folding movements. If this is true, we should 

 expect to find in these districts the equivalents of the Mattagami 

 series resting with structural as well as erosional unconformity 

 on the Grenville. This seems to have been the condition in the 

 Madoc district, where according to Miller the Hastings series, a 

 possible equivalent of the Mattagami series, rests against the up- 

 turned edges of the Grenville.^ 



GRENVILLE ( ?) SEDIMENTS ON THE WEST SIDE OF HUDSON BAY 



While no sediments that can be definitely asserted to be of 

 Grenville age have as yet been described to the west of Hudson 

 Bay, it is interesting to note that there are a number of areas of 

 rocks whose petrography is similar to that of the Grenville series, 

 and which, like them, are intruded by granite apparently of very 

 great age. The reports of Tyrrell and others in this region have 

 yielded a number of more or less doubtful occurrences of these 

 rocks. A few others have been described to the writer by present 

 members of the staff of the Geological Survey. In the vicinity of 

 Lake La Ronge, W. Mclnnes has reported^ crystalline limestones 

 and basic intrusives, greatly folded and altered, and intruded by 

 the granite gneisses of the district. E. L. Bruce has informed the 

 writer that he found ancient garnet and stauroHte gneisses intruded 

 by granites around Wekusko Lake, Manitoba. One of the gneisses 

 anal3^zed is undoubtedly of sedimentary origin. Tyrrell, studying 

 this same area, reports that this gneiss "grades downward into 

 the greenstone schists ' ' ; apparently indicating a conformable rela- 

 tion between the two, similar to that described in this paper. F. J. 

 Alcock states that to the northeast of Lake Athabaska he found an 



^ Kept. Out. Bur. of Mines, Part 2, 1914, p. 12. 

 -Geol. Surv. Can. Mem. 30, 19 13, p. 48. 



