194 THE CANADIAN NATURALIST. [May 



and Goulais Bays. In the majority of instances where the matrix 

 is granular, the fragments are angular ; on the other hand, where 

 the matrix becomes schistose, the fragments are generally rounded^ 

 and there results the slate conglomerate so characteristic of the 

 Huronian series. 



Slate Conglomerate. — This rock is extensively developed at the 

 mouth of the Dore River, some distance to the west of Michipi- 

 coten Harbour. Its matrix is the greenstone slate above described. 

 The boulders and pebbles which it encloses seem, for the most part, 

 to be granite, and are rarely quite round in form. The most 

 of them are oval or lenticular shaped, and then their outlines are 

 scarcely so distinct as in the case oi those which approach more 

 closely to the round form. Very frequently those of a lenticular 

 form are drawn or flattened out to such an extent that their 

 thickness decreases to a quarter or half-an-inch, and they are 

 sometimes scarcely distinguishable from the slate, except by their 

 lighter colour. Part of the rock exhibits merely a succession of 

 lighter and darker coloured bands, the former of which sometimes 

 resemble in form the flattened pebbles above-mentioued. On 

 account of the presence of these lighter bands, it is often impos- 

 sible to select a piece which may be regarded as the real matrix of 

 the rock. As in the case of some of the rocks above described, 

 the light bands are more siliceous and less dense than the darker 

 ones. The latter are, not unfrequently, calcareous. A specimen 

 of this character had a density of 2-708 to 2-802. Its powder 

 was light green, which changed on ignition to light brown, with a 

 loss of 2-75 per cent. On treatment with sulphuric acid, it effer- 

 vesced strongly, and experienced a loss of 36-85 per cent. Iron 

 pyrites impregnates the matrix quite as frequently as calcareous 

 matter. The direction of the lamination in the matrix is parallel 

 with the longer axis of the lenticular pebbles, and where the boulders 

 are large (they seldom exceed twelve inches in diameter) and 

 round, the lamination of the slate winds round them, and resumes 

 its normal direction after passing them. Occasionally a flattened 

 pebble is seen bent half round another, and, among the very thin 

 pebbles, twisted forms are not uncommon. The nature of the 

 pebbles, especially of those which have been flattened, is sometimes 

 very indistinct. The quartz is generally easily recognized in the 

 larger boulders, but the felspar has lost its crystalline character, 

 and the mica is changed into dark green indistinct grains, where it 

 has not altogether disappeared. Besides the granitic pebbles, 



