396 E. M. BURWASH 



However, it affords no evidence of this so far as examined either 

 by lying unconformably on post-Keewatin granites or by the 

 presence of granite pebbles in the conglomerate. Therefore, its 

 assignment to the Lower Huronian would imply either (i) that the 

 granites of this region are all of post-Lower Huronian age, or (2) 

 that the denudation of the great erosion interval which followed, 

 or accompanied and followed, the intrusion of the Laurentian 

 batholiths, was not here enough to uncover the batholiths before 

 the Lower Huronian sedimentation began. If batholithic intrusion 

 took place here in Laurentian time, the batholiths were not uncov- 

 ered until much later perhaps between the Upper and Lower 

 Huronian or even during the Eparachaean interval. Of these two 

 alternatives, the second appears to the writer to be the less probable, 

 judging by comparison with other regions not far distant. Neither 

 alternative would demand the complete absence of Laurentian 

 granite pebbles, since these might have been transported from a 

 distance, and the quartz pebbles, which occur and which are well 

 rounded in contrast to the angular chert-pebbles of Keewatin origin, 

 probably are the residuals of such traveled material. For this series 

 the name of "Birch Lake Series" is suggested. 



3. The granite bodies which were observed in intrusive relations 

 with the Lac Seul (Keewatin) series only are in two cases pink to 

 grayish pink in color. In some parts, usually near contacts or where 

 inclusions of older rocks are abundant, they display a gneissoid 

 texture; in the central parts of the exposed areas and where rela- 

 tively free from inclusions they are more massive. They are also 

 in parts porphyritic. The rocks with which they are found in 

 intrusive contact are frequently cut by dikes of pegmatite, while 

 aplitic dikes as well as pegmatite occur within the mass of the 

 granite itself. The rock is biotite granite with some hornblende, 

 micropegmatite, and microcline, but no muscovite, tourmaline, or 

 titanite. Another type of granite observed in intrusive contact 

 with both the lower (Lac Seul or Keewatin) and upper (Birch Lake) 

 schist series, is of gray color and is practically a binary granite with 

 microcline as the chief feldspar. It also contains a little tourmaline, 

 some oligoclase or andesine, and a little zircon and garnet. In the 

 pegmatite dikes which accompany this granite tourmaline and 



