270 H. C. COOKE 



intrusions. Over a distance of about twenty miles south of its 

 northern boundary the Grenville contains Httle crystalline limestone 

 but is composed almost entirely of altered elastics, largely garnet- 

 iferous. of t3T3es identical or almost so with the Nemenjish series. 

 Farther to the south, where crystalline Hmestone forms a large 

 proportion of the Grenville, much of the remainder is composed 

 of garnetiferous mica gneisses like those of the Nemenjish series. 



A gap of about 140 miles exists between the Nemenjish series 

 and the Grenville, occupied by a great batholith or batholithic 

 complex of granite, which has an east- west extension from near 

 the Bell River at least to Lake St. John, about 250 miles. The 

 correlation of the two series across this belt of granite would 

 appear at first sight a hopeless task; but it is rendered possible 

 by the fact that the eastern end of the batholith is not deeply 

 eroded, in fact is apparently barely unroofed. Across its whole 

 width^ thousands of inclusions of the Nemenjish or Grenville 

 rocks are present, of all sizes and in all stages of digestion. These 

 are so numerous that it is rare to find a single small outcrop of 

 granite without undigested inclusions whose original nature is 

 recognizable. In size the inclusions vary from small lumps a 

 few inches or feet in diameter to large bodies several miles in 

 length, which are probably true roof pendants. In freshness they 

 vary from sharp-angled bodies with little or no trace of the solvent 

 action of the granite to completely dissolved forms now repre- 

 sented by garnetiferous micaceous bands in the gneiss. A very 

 characteristic trade-mark of the interaction of granite and sedi- 

 ment is the presence of garnet, which seems to have dissolved 

 during the digestion of the sediment and subsequently to have 

 recrystallized with little or no change. The formation of such 

 digested products is so well shown in all its stages that even the 

 end products of the reaction might safely be taken as evidence 



' The sections studied by the writer, where such large numbers of garnetiferous 

 inclusions were observed, were those of the St. Maurice River, from the Transcon- 

 tinental Railway to Sandy Beach Lake, and thence northward across the Height of 

 Land to Askitichi Lake; and from the Hudson Bay post at Kikendatch across to the 

 headwaters of the Gatineau, and down the Gatineau. Farther to the west erosion 

 appears to have removed greater thicknesses of granite; correspondingly the num- 

 ber of inclusions become smaller toward the west, and the proportion of those which 

 have undergone complete or fairly complete digestion increases. 



