322 THE CANADIAN NATURALIST. [Vol. VlH. 



only only one or two of these, but as many as nine have been 

 observed in one case. The rude crystals of apatite which are 

 associated with pyrite are cracked across, and the cracks filled 

 with pyrite as shown in figure 5. 



The amygdules have a lining of a green structureless mineral 

 (green earth) while the interior is filled with a colourless mineral 

 which appears in most cases to be calcite. In some cases also 

 the cavities contain pyrites, mostly at the junction of the calcite 

 and green earth. 



VI. 3Iadoc, Ontario, lot 24, Range VI. (Plate, fig. 4.) 

 This rock may be noticed here as a good example of a diorite. 

 It was given to me by Mr. Vennor of the Geological Survey, 

 and stated to have been broken from an undoubted dyke. It 

 was supposed to be a pyroxenic rock, but the microscopic study 

 of a thin section shows it to be a diorite, consisting chiefly of 

 feldspar, hornblende and magnetite, but also containing cubical 

 crystals of iron pyrites and small quantities of a transparent 

 mineral which is probably quartz. The feldspar is a good deal 

 altered, but apparently all plagioclase in the sections examined. 

 The hornblende is of a rich green colour, and much of it shows 

 cleavage lines very distinctly. It is dichroic and polarises 

 beautifully. In places it appears to have undergone some altera- 

 tion, though not to the same extent as the feldspar. 



Conclusions. The first of the rocks just described, on ac- 

 count of the large proportion of viridite which it contains, and 

 the altered state of the feldspar, would be called by German pe- 

 trographers a diabase. One would also expect to find a larger 

 proportion of water than is indicated by the analysis. In many 

 respects it agrees with Senfter's descriptions of diabase from the 

 Duchy of Nassau in Germany. The alteration which it has un- 

 dergone, however, is not nearly as marked as in many diabases 

 from much younger formations, as, for example, the Cretaceous of 

 British Columbia. Much of the viridite looks as if it had been 

 one of the original constituents of the rock, but in other places 

 it is pretty evident that it has been derived from the augitc. 



No. II may perhaps also be called a diabase, although very 

 little removed from such rocks as III and IV. Its general 

 structure is the same, the only important difference being the 

 development of a good deal of viridite. Nos. Ill and IV are 

 true dolerites or "feldspar basalts,'' indistinguishable from many 



