Mr. T. S. Hunt on the Oricjin of some Magnesian Rocks. 377 



magnesium and a little calcium, besides "10 of carbonate of lime and 

 "83 of carbonate of magnesia ; it contains only pj-^ths of its volume 

 of carbonic acid gas. 



In my analyses of the waters of the western basin of Canada,' I have 

 found many brine-springs, which, although rising from Lower Silurian 

 limestones, hold no appreciable amount of earthy carbonates, but 

 contain, besides common salt, large quantities of chlorides of calcium 

 and magnesium ; they are in fact veritable bitterns. The mineral 

 springs of these palaeozoic strata appear to be in all cases connected 

 with undulations producing disruptions of the strata, through which 

 the subterranean waters find egress. In the almost undisturbed 

 region of the west, the springs are consequently rare, but in the 

 disturbed country further east, along the north-western limit of the 

 Green Mountains, which are composed of these same palaeozoic 

 strata in an altered ' condition, the mineral J waters become very 

 abundant. Five or six springs, often differing in kind, may sometimes 

 be found within a short distance along the same line of fault ; but 

 where the strata become crystalline, the mineral waters are no longer 

 met with. 



In this eastern region, the saline waters issuing from the same 

 limestones as the springs just described are generally more dilute 

 than those of the west, and although, like them, containing but very 

 little carbonic acid, deposit by boiling or evaporation large quantities 

 of earthy salts, chiefly carbonate of magnesia. Many of these waters 

 contain earthy rhlorides, and are analogous to the Piillna spring, 

 while others, still strongly saline, are alkaline from the presence of 

 carbonate of soda. The solubility of the carbonate of magnesia in 

 these waters is explained by the observations of H. Rose, who has 

 shown that the partial precipitate produced in the cold, by carbonate 

 of soda in a solution of a neutral salt of magnesia, is redissolved by an 

 excess either of the magnesian s.ilt or the alkaline carbonate, and is 

 only thrown dow^ from these solutions by heat. Longchamji has 

 further remarked that the precipitation by heat is rendered less com- 

 plete in proportion as the carbonate, sulphate or hydrochlorate of the 

 alkali is in excess, and that the precipitate at first formed under these 

 circumstances is redissolved on cooling. I have verified this last 

 observation in the case of these natural waters, from which the mag- 

 nesian carbonate is only separated when they are evaporated to a 

 small volume. When thus evaporated, even at a very gentle heat, 

 these mineral waters yield large quantities of granular carbonate of 

 magnesia, often nearly pure. 



With these facts in view, it is very easy to trace a relation between 

 the saline waters containing carbonate of magnesia, and another class 

 of springs in which tlie predominant element is carbonate of soda 

 with small quantities of common salt, borax, and earthy carbonates. 

 These waters, although wanting in the west, are very abundant in 

 eastern Canada, and rise from the same formations as the saline 

 springs, but are most abundant in the argillaceous strata immediately 

 overlying the lower limestones, which appear to be the source of the 

 salines. These alkaline waters probably owe their origin to the slow 



