GEOLOGY 193 



Ungava bay, where such a separation can be made, and the 

 lighter coloured gneisses are seen to be cut and foliated by the 

 intrusion of the coarser and garnet-free granite-gneisses. At 

 the mouth of Payne river and about the mouth of Hopes Ad- 

 vance bay the change from unaltered clastic rocks to the light- 

 coloured gneisses is plainly seen in a number of places. The 

 unaltered series consists of impure dolomites, sandstones, cherts 

 and bedded iron ores similar to the series of rocks found in the 

 central parts of Labrador and along the east coast of Hudson 

 bay. This series bears a close resemblance to the iron-bearing 

 rocks of Lake Superior, and there is little doubt that they are 

 of the same age. In former reports they have been termed so- 

 called Cambrian, but by the new classification they represent 

 one or more members of the Huronian. These rocks are asso- 

 ciated, as elsewhere, with great outbursts of basic igneous 

 matter in the form of sills, dikes and irregular masses. Where 

 the newer granites have cut and inclosed masses of this series, 

 the different rocks forming it are seen to have undergone con- 

 siderable alteration. The bedding has been disturbed, so that 

 the strata lie at angles approaching the vertical, and have been 

 broken, and minutely penetrated by quartzose injections, both 

 along and across the bedding planes. Foliation and schistosity 

 have been induced, and the arrangement of the chemical con- 

 stituents has been altered so that new minerals are formed. 

 The impure cherty limestone is changed to hornblendic schists, 

 the impure sandstone and quartzite to garnet-bearing quartzose 

 gneisses, and the cherty iron ores to a gneissic rock consisting 

 of layers of quartz and specular iron. 



An examination of a number of the contacts between the 

 granites and the Huronian rocks shows an alteration, from a 

 slight crumpling and baking to highly tilted and contorted 

 crystalline schist and gneiss. The accompanying basic igneous 

 rocks, originally fine-grained traps or diabase, are changed in 



