PRE-CAMBRIAN FORMATIONS— ONTARIO AND MANITOBA 463 



Porcupine lake in lot 1 1 in the fourth concession of Whitney there is a contact 

 of the sedimentary series with pillow lava in which the relationship suggests 

 an igneous contact, that is that the pillow lava is later than the sedimentarj'- 

 rock. It is therefore probable that some of the pillow lavas mapped with the 

 Keewatin are later in age than the Temiskaming series. 



While there is much evidence pointing to a separate sedimentary series 

 of rocks the possibility of some of what has been called Keewatin being 

 contemporaneous with the Temiskaming or of some of the sediments being 

 of Grenville age must be considered. Toward the southwest from the open 

 pit at the Dome mine there is a narrow band of conglomerate which has been 

 mapped at Temiskaming. Much of the material in this band immediately 

 north of the readily recognized pillow lava and amygdaloidal rock resembles 

 volcanic fragmental or agglomerate. There is no break, however, between 

 the apparent volcanic fragmental and the interbedded slate and greywacke 

 which occur along the south margin of the open pit and which can be followed 

 northward for a mile. If the rock above mentioned is a volcanic fragmental, 

 and not a true conglomerate deposited on an eroded surface, then there is 

 reason for considering the pillow lavas, fragmental rocks, slates, greywacke 

 and conglomerate as belonging to one series. For lithological reasons' it seems 

 preferable to consider the large area of sediments as a separate series. 



It is apparent that Burrows recognized the possibility of an 

 interbedded series of sediments and volcanics, but that he decided 

 to correlate the sedimentary part of the series with the lithologically 

 similar Temiskaming rather than accept an alternative hypothesis 

 of a great continuous series made up of lava flows, volcanic frag- 

 mentals, and true sediments. The evidence for an erosional 

 unconformity between the volcanics and sediments does not 

 seem to be conclusive. 



ABITIBI DISTRICT 



The district south of Lake Abitibi has recently received con- 

 siderable attention, and an interesting series of rocks has been 

 found.^ Lava flows which are classed as Keewatin are exceptionally 

 well developed, and the scoriaceous surfaces of successive flows 

 make it possible to determine the top and bottom of the forma- 

 tions. Sediments are associated with these lavas. The following 

 is a quotation from the report mentioned: 



^ C. W. Knight, A. G. Burrows, P. E. Hopkins, and A. L. Parsons, "Abitibi Night 

 Hawk Gold Area," Eighteenth Ann. Rept. Ont. Bureau oj Mines, Part II (1919). 



