GRANITIZATION OF ACIDIC LOWER HURONIAN SCHISTS 235 



from east to west. This batholith is joined to the main part of the 

 acid eruptive complex by a narrow band of granite, which separates 

 the Michipicoten Huronian area from the Pucaswa Huronian area. 

 Another off-shoot from the bathoKth further divides the Pucaswa 

 area. 



The oldest rocks visible in both the Pucaswa and the Michipicoten 

 areas are the so-called Lower Huronian. Above these lie Upper 

 Huronian rocks which, though somewhat rare in the Pucaswa area, 

 have abundant outcrops in the Michipicoten area. Cutting both 

 Lower and Upper Huronian are granites and allied rocks, which have 

 frequent outcrops in the shape of bosses and dykes, within the limits 

 of the Huronian rocks proper, and which have also already been 

 mentioned as forming the boundaries of the Pucaswa and Michipi- 

 coten areas. Piercing both the Huronian rocks and the granites 

 are basic igneous rocks of somewhat varied lithological composition, 

 which are very probably Keweenawan. 



The Michipicoten Lower Huronian may be subdivided into two 

 divisions — the Helen Iron Formation and the Michipicoten schists. 

 The same rocks in the Pucaswa area may be similarly resolved into 

 an Iron Formation and schists. The Iron Formation in the Michi- 

 picoten area and in the Pucaswa area may be regarded as the only 

 definite horizons within the Lower Huronian of the areas. Above 

 and below these formations lie the schists. In the Michipicoten 

 area, and particularly in that part which lies west of the Magpie 

 River, a very close connection between the Upper Huronian rocks 

 and the Helen Formation is observable. The latter, generally, very 

 closely underlies the Dore Formation which in Michipicoten makes 

 up the Upper Huronian, but in some parts of the area thick masses 

 of schists intervene between the Helen Formation and the Dor^ 

 Formation, indicating either an unequal denudation of the Lower 

 Huronian previous to the deposition of the Dore rocks, or otherwise 

 an unequal deposition of volcanic material after the Helen iron- 

 bearing rocks have been laid down. In some places the width of 

 the Helen rocks appears to diminish, and at the same time there is a 

 relative increase in the amount of schist which seems to suggest that 

 in these parts of the area, toward the close of Lower Huronian times, 

 chemical and aqueous sedimentation was overpowered by volcanic 



