462 E. L. BRUCE 



to have been no erosion period between the formation of the two 

 series. 



Lawson considered the Coutchiching to be a distinct series 

 underneath the Keewatin, but the international committee to 

 revise the classification of pre-Cambrian formations did not agree. 

 In some of the areas examined rocks mapped as Coutchiching in 

 the original work were found to belong to the Seine series, which 

 lies with a great unconformity above the Keewatin. Mistakes of 

 this kind are quite to be expected in determining somewhat similar 

 series under the difiicult conditions of the original mapping. Law- 

 son, in his later publication, Memoir 40, Geological Survey of 

 Canada, admits these mistakes, but still maintains that there is a 

 great sedimentary series below the Keewatin. Some competent 

 observers who have visited the area agree with him,^ The point 

 has also been raised that the Coutchiching may not be the oldest 

 formation, but may be similar to the interbedded sediments — (12) in 

 the Keewatin — and that beneath the Coutchiching again there 

 may be still older lava flows. If so, it is argued, the Coutchiching 

 series may quite logically be included as part of the Keewatin. 



PORCUPINE DISTRICT 



The earhest rocks in the Porcupine district of northern Ontario 

 consist of pillow lavas with schists derived from them, "carbonate" 

 rocks of doubtful origin, iron formation, and some fragmental 

 rocks of doubtful character.^ A group of undoubtedly sedimentary 

 rocks is correlated by Burrows with the Temiskaming series. 

 They consist of "conglomerate, interbanded slate and gre3nvacke, 

 and quartzite." The relations of these sediments to the Keewatin 

 group are shown by the following quotations: 



A contact of the sedimentary rocks with the volcanic rocks can be seen 

 immediately south of the open pit at the Dome mine. Fragments of the 

 volcanic series are abundant in the sedimentary series, and it is likely that 

 the conglomerate has been deposited on the surface of the volcanic series of the 

 Keewatin However, one half a mile north west of the north end of 



^ Private Communications, F. J. Alcock and T. L. Tanton. 

 2 A. G. Burrows, "The Porcupine Gold Area," Third Ann. Rept. Out. Bureau of 

 Mines, Vol. XXIV, Part III (1915). 



