44 THE CANADIAN NATURALIST. [Marcll 



with hydrochloric acid, which separated sihca, which was after- 

 wards dissolved out from the insoluble by weak potash lye. It 

 was found to contain : — 



Silica 45 ■ 13 



Alumina 33 '92 



Lime 17 02 



Insoluble 4 '46 



100-53 



The mineral probably contains also a small quantity of soda, as 

 it colours the blow-pipe flame strongly yellow. The anorthite 

 crystals frequently contain small brownish specks, and the matrix 

 of the rock consists of a small-grained mixture of these with the 

 anorthite. Sometimes a larger individual is perceived with a 

 brownish black colour and glittering faces, and, besides such, there 

 are dark green grains of chlorite, and occasional specks of iron 

 pyrites. A piece of the rock, weighing 30'455 grammes, had a 

 specific gravity of 2-806. 



The influence of these dykes upon the bedded strata which 

 they intersect is very marked. Both the argillaceous and the 

 dolomitic sandstones become hardened and silicified, and enabled 

 much more effectually to resist disintegrating influences. In many 

 places, where they have been much acted on by the waters of the 

 lake, the altered part of the sandstones is found remaining and 

 adhering to the dyke, while traces of the unaltered strata are 

 visible only among the debris on the shore. Instances are also to 

 be found where the bedded strata have been much contorted in 

 the neighbourhood of the dykes. One instance was observed of 

 the rock of a dyke enclosing fragments of granite and quartzite, 

 the longer dimensions of which run parallel with the side of the 

 dyke. This dyke is the first one met with on the shore to the 

 west of Boulder Point. 



There are numerous veins on the location, connected, for the 

 most part, with the dykes which have just been described. It 

 may be doubted whether these veins, the most of which are 

 indicated upon the map, possess in every case the characters of 

 true metalliferous veins. Some of them appear to be mere 

 fillings up of the separation joints in the rock of the dyke. 

 Others, which appear more promising, are of greater width, and 

 run parallel with the dykes, but were not observed to contain 

 anything more valuable than specks of iron and copper pyrites. 

 A third variety of vein, which is perhaps the most important, 



