Lawson.] 



Ma lignite. 



339 



The shores of the lake are occupied for the most part by a 

 coarse syenite-like rock which is intrusive in the mica schists of the 

 Coutchiching series of the Ontarian system of the Archaean. This 

 intrusive mass has a roughly elliptical shape in ground plan, with a 

 longer diameter of not less than six miles, and a shorter diameter 

 of about three miles. It has the same intrusive relation to the 

 Goutchiching schists as do the normal Laurentian biotite granites 

 and hornblende granites and their gneissic modifications. The 

 mica schists strike around the mass so as to inclose it on all sides 



Figure i. — Sketch map of Poohbah Lake; showing relation of the laccolite 

 mass to the Coutchiching schists. A. nepheline-pyroxere- 

 malignite; B, panidiomorphic-gneissic- fades of the same; C. 

 garnet-pyroxene-malignite; D, a minor facies of the same; E. 

 amphibole-malignite; F, Coutchiching schists. The numbers 

 495> 5 OI > 5°3> 5°6) and 510 indicate where specimens were 

 taken. Scale, two miles=one inch. 



The schists are well exposed on the north side of the lake and at its 

 southwest extremity; and the known distribution of the same rocks 

 in the region to the north, west, and south of the lake is ample war- 

 rant for the approximate delimitation of the intrusive mass indi- 

 cated on the accompanying diagram, Fig. r. To the northwest of the 



