174 MINERALS AND GEOLOGY 



strata south of the St. Lawrence. In the latter district, as already 

 mentioned, some of these limestone beds are intermixed with green 

 and other coloured serpentines, but many of the so-called serpentine 

 marbles from the Eastern Townships are mixtures of serpentine with 

 dolomite or magnesite. 



Crystalline Dolomite : This rock resembles crystalline limestone 

 in colour and other external characters, but consists of carbonate of 

 lime and carbonate of magnesia, and only effervesces when tested 

 with heated acid (See Part I). It occurs, here and there, amongst 

 the Laurentian strata, as at Lake Mazinaw in the County of 

 Frontenac, and elsewhere. Also among the strata of the Eastern 

 Townships, in which district beds of crystalline magnesite (See Part 

 II), mixed with mica, serpentine, &c., are likewise present. These 

 magnesian beds, as pointed out by Dr. Sterry Hunt, assume a 

 yellowish or dull-red colour by weathering. 



Crystalline Iron Ores : Vast beds of Magnetic, Specular and 

 Titaniferous Iron Ore, occur locally amongst the rocks of the Laur- 

 entian series, and should thus be referred to in connexion with the 

 metamorphic formations of Canada. The strata of the metamorphic 

 region south of the St. Lawrence are also especially characterized in 

 certain localities by the presence of chromic iron ore in rock masses ; 

 and many of the chloritic and other schistose strata of this region 

 pass locally into "iron slates" or "specular schists," by the addition 

 of micaceous hematite or specular ore. The distinctive characters of 

 these Iron Ores, and their principal localities, are given in Part II. 



IV. MASSIVE OR UNSTRATIFIED HOCKS. 



The rocks of this division are commonly known as Igneous or Erup- 

 tive Rocks. With regard to the igneous formation of certain members 

 of the Eruptive Series, there can be no possible doubt ; but the actual 

 mode of formation of other rocks of this group is involved in great 

 obscurity. All agree, however, in being essentially devoid of true 

 planes of stratification. They occur either in irregular imsfcratified 

 masses ; or in sheets or apparent beds, intercalated amongst, or over- 

 flowing, stratified deposits ; or in the form of more or less tortuous 

 veins ; or in broader and simpler veins, technically known as 

 "dykes," which frequently terminate at their upper extremity in 



