REVIEWS — GEOLOGICAL SURVEY OF CANADA. 333 



du Loup. Notices of the more important of these topics, as treated 

 by Mr. Hunt, have already appeared in the pages of this Journal. 



The second Report is one of much scientific interest. It comprises, 

 in the words of Mr. Hunt, " a series of investigations of the stratified- 

 crystalline or metamorphic rocks of the country, undertaken in the 

 hope that a careful comparative study of their composition, in con- 

 nection with that of the unaltered sedimentary strata, may lead to the 

 clear understanding of the nature of that metamorphic process whose 

 results are so conspicuous in our Canadian geology." In the prosecu- 

 tion of this inquiry, a considerable number of complex analyses are 

 given, the value of which will become still more apparent, as the sub- 

 ject is more fully developed. The labradorites and triclinic feld-spars 

 of the Laurentian rocks generally, are considered by Mr. Hunt — in 

 accordance with the opinion of Delesse, respecting these so-called 

 species from other localities — to consist of mixtures of Albite and 

 Anorthite in variable proportions. As these minerals, however, in- 

 cluding albite and anorthite, agree so closely with one another in 

 crystalline form, we might here adopt the view of one fundamental 

 composition (= a? R O, a; Al ^0^, x SiO^) combined with additional 

 atoms of silica — Si O ^, 2 Si O ^, &c, — according to the species or, 

 more properly, the variety : these additional atoms being held, further- 

 more, to be without influence on the crystallization of the compound, 

 although necessarily affecting its comportment with chemical reagents. 

 This view is apparently shadowed out, though not exactly stated in 

 this manner, in the fourth edition of Dana's Mineralogy, vol. 2, 

 page 228. 



The observations which we give below, on the manufacture of 

 hydraulic mortars with magnesia in place of lime, are extracted from 

 the Report for 18.55, in which Mr. Hunt has also published some long 

 and important communications on the Metallurgy of Iron, in explana- 

 tion of Chenot's Process, the Extraction of Salts from Sea "Water, 

 and other subjects of much practical interest : 



MAGNESIAN MORTAES. 



The attention of several chemists has been of late years turned to the study of 

 cements and mortars, but it is especially to the laborious and admirable researches 

 of M. Vieat of Grenoble, that we are indebted for a complete elucidation of some 

 of the most important questions connected with the subject. The ordinary mortars 

 composed of lime and sand, harden gradually by exposure to the air, and this pro- 

 cess depends upon two distinct reactions ; first, the absorption of carbonic acid. 

 from the air, and the formation of a sub-carbonate of lime, and secondly, upon a 

 partial combination of the lime with the sand, forming a silicate of lime. When 



