121 



close of the Pre-Cambrian and the opening of the Paleozoic 

 era. 



The Pre-Cambrian portion of this district presents an 

 undulating but not greatly elevated topography. The 

 average elevation is about 500 feet (152m) above sea-level. 

 There are so few exceptions to this, that the whole country 

 presents an almost level sky-line, with few if any projections 

 rising notably above the rest. The area is dotted with 

 lakes, occupying from one-third to one-half of the whole 

 area; only a few of these have been mapped, but the result 

 is striking in bringing out their north-easterly elongation. 

 This is governed by the strike of the gneisses of which the 

 area is largely composed, and not by glaciation as might 

 be suggested. This north-east and south-west system of 

 drainage is characteristic of the whole ' ' Laurentian 

 Peneplain," as a glance at the map of Eastern Canada will 

 show. 



The Pre-Cambrian area under consideration on this 

 excursion consists of the typical Laurentian, together with 

 the Grenville phase of the Keewatin. The recent work of 

 Adams [1], Barlow [2], Miller and Knight [3] would indi- 

 cate that the Grenville is made up largely of highly meta- 

 morphosed sediments, and this probably accounts for the 

 great variety of well-individualized minerals developed 

 throughout this area. The whole Pre-Cambrian complex 

 is so intensely metamorphosed and infolded, that with 

 the exception of the crystalline limestones, it is not easy to 

 distinguish the Grenville from the Laurentian metamorphic 

 rocks. 



The whole district consists essentially of gneisses, 

 In some localities their foliated character is so faini that 

 they might be called granites. These gneisses differ very 

 markedly among themselves in the proportion of their 

 constituents. The typical rock consists of quartz, ortho- 

 clase, and biotite, but in many places hornblende takes the 

 place of the biotite; or the quartz becomes so abundant 

 that the rock might be mistaken for a quartzite; or the 

 feldspar so predominates, that the rock passes into a 

 syenite gneiss. Seldom over any great area do the rocks 

 maintain the same composition, and the minerals enter 

 into their composition in every conceivable proportion. 



It is probably safe to conclude that the distinctly 

 lightly coloured, grayish to reddish psamitic gneisses, rich 

 in hornblende, belong to the Laurentian, as in the case of 



