On the Minerals of Canada. 57 



of the quarries are wrought on rocks of the same geological epoch 

 as those which underlie the clay on which Toronto is built, altered 

 however by heat. The numerous applications of this entirely useful 

 material have been alluded at some length by Sir W. Logan in his 

 Geological Report : 



" Not only is it applied as a covering for houses, but it is em- 

 ployed as walls for cisterifis to hold water, slabs of fifteen feet by 

 eight feet being sometimes used for the purpose : in smaller dimen- 

 sions, it is used for wine coolers, dairy dressers, kitchen and hall 

 •flooring, tables, chimney mantles, and a multitude of other purposes 

 where surface is required. In its application as tables and chimney 

 pieces, it is capable of receiving a great degree of decoration ; the 

 tables after being dressed to the smoothest possible surface, are 

 embellished with gilding or with paintings in colors resisting fire, 

 showing landscapes, or imitations of stone, and a silicious varnish 

 being applied, the stone subjected to a heat which melts the varnish 

 into an enamel, and produces a brilliant result. Chimney pieces in 

 the same way are enamelled over the natural colour of the stone, 

 or over a fancy colour given to it. When the colour is black, it 

 is difficult to distinguish the slate from a brilliantly polished and 

 valuable black marble, while the cost is comparatively small. The 

 great number of purposes to which good slate is applicable, render 

 the rock of great economic importance, and well worthy of research." 



HYDRAULIC LIMESTONES. 



The term hydraulic limestone is very frequently met with in 

 accounts of the construction of reservoirs, canals, water-tanks, 

 cellars, and a host of other artifices of public utility and domestic 

 comfort. Often, indeed, these fail to secure the object for which 

 they are designed, as many of the public works in the United States 

 testify. This arises from a misconception of the nature of an hy- 

 draulic limestone, and of the eff'ect which time and exposure are 

 capable of producing upon different varieties. This subject has 

 been much studied in Europe by the ablest chemists, but not with 

 those clear and satisfactory results which so frequently distinguish 

 the progress of modern science. Mortars and hydraulic cements 

 may.be thus distinguished : — 



1. Common limestone, such as the limestone from Kingston, or 

 the quarries on the western extension of the Grand Trunk, is expo- 

 sed to a heat suflScient to drive off the carbonic acid it contains ; it 



