56 On the Minerals of Canada. 



tion, these limestones become more crystalline, and form tlie wliite 

 marbles of Vermont, whicli are now celebrated. The upper Silu- 

 rian limestone of Dudswell are greyish and yellowish, with veins 

 and spots of black, they still exhibit on their polished surfaces, the 

 traces of fossils, and often form marbles of great beauty. 



The specimens upon the table were from Madoc ; a considerable 

 abundance of coarsely crystalline marble occurs in those back 

 townships, and as the country becomes cleared and known, more of 

 better quality will probably be found. 



The process of turning and polishing marbles by means of a com- 

 mon lathe is not generally known, and may therefore be briefly 

 noticed. A piece of marble of the size required is selected free 

 from veins and cracks. The first operation is to chisel it roughly 

 to a cylinder form. It is then fastened by resinous cement to the 

 lathe and subjected to a slow revolving motion. The tool used is 

 a bar of iron about 30 inches long and pointed, this is forcibly 

 applied to the revolving cylinder of marble, which it gradually re- 

 duces to its required form. A coarse sandstone with plenty of 

 water is next applied ; the cylinder of marble being made to re- 

 volve much more quickly. The tool marks disappear under this 

 process. A finer piece of sandstone is then employed to remove 

 the scratches of the preceding one, and so on with still finer stones, 

 until all scratches are quite obliterated. In polishing, a piece of 

 of cotton cloth rubbed with flour emery is used ; and, finally, a 

 similiar piece of cloth rubbed over with tin putty gives a very 

 high polish, and completes the process. 



SLATE. 



Slate is a material daily becoming more valuable on account of 

 the vast variety of useful purposes to which it is applied. One of 

 its most important characteristics is its strengh, it is computed to 

 be about four times as strong as ordinary stone, and slabs 8 feet 

 long and upwards can be safely used of thicknesses not exceeding 

 half an inch. It is a non-absorbent of moisture and thus adapted 

 as a admirable lining for wells and for roofing houses. The slates 

 which were taken to the London Exhibition from Canada were 

 not good representations of the material since found to exist in this 

 country. The economical importance of slates has attacted atten- 

 tion to their distribution in Lower Canada, and already large 

 quarries are worked which farnish slate of superior quality. Some 



