40 THE CANADIAN NATURALIST. [Murcll 



on page 70 of the Geology of Canada. This rock is fine- 

 grained and compact, generally of a yellowish grey colour, with 

 red patches. Where the latter colour predominates, the rock 

 assumes a slaty structure. The reddish-coloured spots or patches 

 have generally a rounded contour, and although they sometimes 

 resemble rounded fragments or boulders, it is found, on breaking 

 them, that they consist of the same fine-grained material as the 

 marl itself, diifering from it only in colour. Occasionally, other 

 enclosures occur in this rock, which seem more distinctly separated 

 from it, some of them resembling pieces of the shaly sandstones of 

 the lower group, but purple coloured. They are doubtless of 

 a fragmentary nature. Specimens of indurated marl from Island 

 No. 6 were subjected to analysis, the light coloured (I) and 

 reddish portions (II) being examined separately. 



I. II. 



Silica (insoluble in Hydrochloric Acid and Potash lye). . 5077 53-27 



Peroxide of Iron and Alumina 2-48 5'78 



Carbonate of Lime 34'43 21-00 



Carbonate of Magnesia 7-68 1343 



Silica 3-28 3 48 



Water i'7g 2-04 



100-43 99-00 



On the eastern extremity of the location, the indurated marl is 

 overlaid by white sandstone again, and this rock appears to be the 

 highest in geological position upon the property. 



These stratified rocks are intersected by numerous dykes of 

 various thicknesses, running generally parallel with each other in 

 a north-east and south-western course. Their outcrops are most 

 numerous in the western part of the location, where they, and the 

 enclosing argillaceous sandstones and shales, have been so acted on 

 by the waters of the lake as to expose plainly their mutual 

 relations. The dykes are coloured green on the map, and it will 

 be plainly seen from it, that they, to a very considerable extent, 

 determine the outline of the shore. The longer lines upon the 

 coast run generally parallel with the strike of these dykes ; the 

 hard rocks of the latter invariably form the projecting points and 

 headlands, while the bays are cut out of the softer stratified 

 rocks. Although the dykes are best exposed among the grey 

 sandstones, many of them can be followed into the area occupied 

 by the red and white sandstones, where they are found to inter- 

 sect these also. They are always either vertical or inclined at 



