126 Macfarlane on the Primitive Formations 



sometimes very chloritic. In a third form, the matrix is scarcely 

 distinguishable from a fine grained greenstone In the slate, the 

 stratification is often marked by slight differences of color, in the 

 direction of which, it is occasionally clcavable. The bands in 

 other instances, are firmly soldered together, but in both cases, 

 joints usually prevail, dividing the rock into rhomboidal forms, 

 which are sometimes very regular." 



These slates sometimes approach to argillites, but often, through 

 the chloritic varieties, appear to pass into greenstone or diorite, 

 which, in its typical form, consists of a greenish white feldspar, 

 with dark green or black hornblende. The feldspar is sometimes 

 however, more or less tinged with red, and the rock then occa- 

 sionally appears to pass into a kind of syenite, by the addition of 

 a very sparing amount of quartz. These two forms of the rock 

 are generally highly crystalline, and not very fine grained. The 

 greenstone, however, sometimes displays a fine texture ; and in 

 such cases it frequently holds much disseminated chlorite, giving 

 it a very decided green colour. Portions are found, containing 

 so great a proportion of the mineral, as to yield with facility to 

 the knife. 



Associated with these, are three bands of impure limestone, 

 often silicious and sometimes dolomitic, the uppermost one of 

 which, is interstratified with a large amount of hornstone, in 

 very regular beds. The total thickness of the formation on 

 Lake Huron, is estimated about 18,000 feet; of which more than 

 10,000 feet are quartzites, including the jasper conglomerates. 

 900 feet of the remainder are hmestone and hornstone bands, and 

 the remainder the slate conglomerates, with chloritic and epidotic 

 slates the whole being interstratified with diorites. 



While the great mass of these greenstones or diorites, are sup- 

 posed to be altered sedimentary beds,there are other greenstones, 

 which, as well as certain granites in the formation, are evidently 

 intrusive. 



The most important mineral deposits of the Huronian series 

 are the copper lodes at the Bruce, Wellington, and Huron Bay 

 mines. The ores are here yellow and purple sulphuret, in veins, 

 of quartz, which cut the diorites of the region. According to Sir 

 W. E. Logan's careful examination of the Bruce Mines, made in 

 1848, about 3000 square fathoms of the lodes were computed to 

 contain, on an average, 6^ per cent, of copper. Since then, about 

 9000 tons of 18 per cent, ore have been raised from the mine, 

 which has been opened to a depth of 50 fathoms. Attempts 



