28 TyE Ottawa Naturalist. [May 



others as magnesian micas, of which the biotite differs in con- 

 taining iron as well, and is consequently darker in colour and 

 sometimes quite black. The muscovite is distinguished by its 

 general clearness and lack of colouring, while the phlogopite 

 mica is usually some shade of brown or yellow and is generally 

 known as amber mica. Years ago large sheets of white mica, 

 as it was generally styled as contrasted with the darker coloured 

 or amber variety, were quoted at a very high price, but this dis- 

 tinction seems of late years to have largely disappeared, as is 

 also the case wnth sheets of extra large size, since this feature of 

 size is now attained by a process already referred to of building 

 up by means of cement and pressure from smaller sizes, so that 

 almost any size required can now be readily obtained. 



Of these several varieties, the white or muscovite is usually 

 found in association with intrusive n?asses of a whitish granite, 

 composed of quartz and white felspar which cuts the gneiss 

 and limestone in the form of dykes or veins ; while the amber 

 and black varieties are found in connection with pyroxenes. As 

 a rule the darker the containing rock the blacker the mica, so 

 that in the light coloured pyroxenes the mica is often a light 

 shade of amber. The most perfectly shaped crystals are 

 generally found in a matrix of calcite in the pyroxene ; and were 

 it possible to secure perfect crystals at all times there would be 

 much more profit in mica mining than has yet been enjoyed. 

 Unfortunately, however, the greater portion of the crystals are 

 injured by wrinkles, cracks, small punctures or from some other 

 cause, so that it is a fortunate mine that will yield ten per cent, 

 of merchantable mica from its total output. 



Crystals are often found in the Gatineau district of very 

 large size, one from a mine near the Cascades being stated to 

 have a diameter of nearly eight feet. Unfortunately thes2 large 

 crystals, owing to their generally fractured condition, have 

 generally but little economic value. One of the largest deposits 

 of this mineral yet found in the Gatineau district is in the town- 

 ship of Hincks. It occurs in a dyke of pyroxene which cuts the 

 limestone of that area and is in turn cut by a dyke of green- 



