REVIEWS — GEOLOGICAL SURVEY OF CANADA. 335 



lime. The theory of the solidification of these yarious cements, and the important 

 part played by the alkali which is always present, in forming a silicate of lime, has 

 been carefully studied by Kuhlmann and Fuchs ; the application of soluble glass 

 for the silicatisation of limestones and other calcareous materials, depends upon a 

 similar reaction. But important as is this question, both in a theoretical and prac- 

 tical point of view, I shall reserve it for another occasion. 



The cements prepared by the different processes above indicated, leave nothing 

 to be desired for constructions in fresh water, but do not uniformly resist the 

 action of the sea, which causes a great many of these hydraulic cements to lose 

 their cohesion, and eventually fall to pieces when immersed in sea-water. M. 

 Vicat, junior, has found that this change depends upon the action of the magnesian 

 salts of the sea-water upon the lime of the cement, and has proposed a mortar from 

 which lime is excluded, consisting of caustic magnesia mixed with an artificial 

 pozzuolana. For this purpose such materials should be selected as contain no 

 calcareous matter, and he recommends pipe-clay, or the debris of certain felspathic 

 rocks. These when calcined and mixed with 15 or 20 per cent, of magnesia, pi'e- 

 viously made into a paste with water, yield a cement which hardens after three or 

 four days, either under fresh or salt water, and acquires after some time a great 

 degree of strength. 



But important as this discovery of Mr. Vicat promises to be, the high price of 

 magnesia is opposed to the general adoption of this cement to marine constructions. 

 The inventor calculates that if magnesia can be furnished for $30 or $40 the ton, 

 the cement ean be economically made use of, and the directors of the salines of the 

 south of France are now endeavoring to manufacture magnesia on a large scale, 

 from the chlorid of magnesium in the bittern of the sea- water. Carbonate of 

 magnesia is abundant in nature, but almost always found united with carbonate of 

 lime, forming a dolomite, and the pure magnesian carbonate has hitherto been a 

 Tare mineral. Associated with a Kttle carbonate of iron and some silicious 

 matters, however, it is found in abundance in the Eastern Townships, where it 

 forms beds among the Silurian slates in Sutton and Bolton. Specimens of it from 

 these localities attracted particular attention at the Exhibition at Paris, where the 

 magnesian mortar of Vicat was first brought forward, and the Reporter of the Jury 

 of the 14th class calls particular attention to the value of this mineral as a source 

 of maguesia, and as possibly destined to become an article of export from Canada. 



The magnesite from Bolton, where it forms an immense bed, resembles a crystal- 

 line limestone, and consists of about 60.0 per cent, of carbonate of magnesia, 9.0 

 per cent, of carbonate of iron, and 31.0 of quartz in grains, besides small portions 

 of nickel and chrome. Some specimens from Sutton contain more than 80.0 per 

 et. of carbonate of magnesia. When this mineral is calcined, the carbonic acid is 

 expelled, and there remains a mixture of magnesia with quartz and oxyd of iron. 

 But as these impurities do not interfere with its application to the purposes of a 

 cement, the previously ignited rock, which in the case of that from Bolton will 

 contain 43.0 per cent, of caustic magnesia, may be directly mixed with calcined 

 elay or pozzuolana, to form the magnesian mortar. Although it is not certain 

 that these native carbonates can be economically wrought for exportation, the sub- 

 ject is certainly worthy of the attention of our engineers who are engaged in the 

 construction of docks and piers in the lower ports of the St. Lawrence. At the 



