i8 FRANK D. ADAMS 



underlain by basic and acid volcanics, porphyrites, and porphyries. 

 These sandstones and volcanic rocks are, by the Canadian survey, 

 classed provisionally as of pre-Cambrian age and it seems not improb- 

 able that they are later than the groups of rocks about Great Bear and 

 Great Slave Lakes which have been correlated with the Nastapoka 

 series. Thus it is possible that the Athabasca sandstones and asso- 

 ciated volcanics are the northern representatives of the Keweenawan 

 of Lake Superior, concerning whose pre-Cambrian age there is a 

 similar doubt. 



These sandstones are composed chiefly of quartz grains which 

 it has been supposed have been largely derived from a series of 

 quartzites known as the Marble Island quartzites and which on the 

 western shores of Hudson Bay occur at intervals over a stretch of 

 about one hundred and twenty miles. These are associated with 

 masses of dark schists, etc., lying in a disturbed condition. The 

 presence of siliceous material in the widespread Athabasca series, 

 so like that composing the quartzites, would seem to indicate that 

 these latter were at one time also widely developed. What their 

 equivalents elsewhere are, if they have any, is not yet known. 

 They apparently are older than both the Athabasca and the Nastapoka 

 series and may belong to some division corresponding to the earlier 

 Huronian. 



The rocks of the Athabasca-Keweenawan series are unaltered and 

 lie practically flat. They have not been affected by orogenic dis- 

 turbances or deep-seated plutonic intrusions. The uplift which raised 

 them from the waters of the ocean was epeirogenic in character. 

 Since the close of the pre-Cambrian, the continent of Laurentia, 

 while preserving its character as a positive element, has undergone 

 many oscillations, but orogenic or mountain-making forces have never 

 manifested themselves, and the successive epeirogenic uplifts have 

 resulted in and to a certain extent been compensated by the deep and 

 long-continued erosion to which the continent has been subjected 

 throughout the greater part of post-Proterozoic time. 



Using therefore the epochs of diastrophism, which mark the suc- 

 cessive stages in the pre-Cambrian development of the continent, 

 as a basis of correlation, provisionally grouping the Athabasca Sand- 

 stones with the Nastapoka series, it would appear that we have three 



