192 



MINERALS AND GEOLOGY 



but the scope of the present work admits only of a general i 

 to this subject.* 



Mineral veins may be denned as cracks or fissures in the Earth's 

 crust, filled or partially filled with stony and metallic matters. In 

 some veins, stony or sparry matters, as quartz or calc spar, are alone 

 present ; but these matters are very generally accompanied by metallic 

 sulphides, oxides, or other compounds, and occasionally by native 

 metals. The sparry or stony substances are then known as gangues 

 or veinstones. The more common veinstones comprise : quartz, calc 

 spar, fluor spar, and heavy spar two or more of these being frequently 

 present together. In the higher part of a vein, frequently to a depth 

 of several fathoms from the surface, the gangtie and ores are often in 

 a partially decomposed or earthy condition. 



A mineral vein thus forms a more or less compressed sheet of mineral 

 matter, extending often to unknown depths, and being frequently 

 traceable for several miles across a line of country. Some veins are 

 less than an inch broad, whilst others occasionally exceed twenty or 

 even fifty feet in width. Many of the veins containing native silver 

 in the district around Thunder Bay on Lake Superior, are at least 

 twenty feet wide, and some are wider. A vein of calc spar, carrying 

 galena, at the Fronteiiac Mining Location in the Township of Lough- 

 borough (north of Kingston) is very nearly as wide, although the 

 workable portion is limited to about twelve feet in breadth. As a 

 general rule, however, few veins exhibit a greater average width than 

 three or four feet ; and in nearly all cases a vein contracts and expands 

 more or less at different depths, or in different parts of its course. 

 Many veins traverse the enclosing rocks, or "country," almost or quite 

 vertically ; others incline at a greater or less angle, the inclination 

 being commonly termed the "underlie" or "hade;" and some again 

 run almost horizontally, or like a narrow bed, for certain distances. 

 The sides of a vein are known in mining language as the walls. These 

 are very often separated from the enclosing rock by a band of brown 

 ochreous matter or gossan, arising from the decomposition of pyrites, 

 or by a layer of clay or other soft or earthy material. This is techni- 



* Although true veins are of not uncommon occurrence among Canadian rock -formations, 

 it should be premised that many of our metalliferous deposits, our iron ores especially, are 

 chiefly present in the form of large irregular masses or "stocks." 



