172 



MINERALS AND GEOLOGY 



some varieties are dull chocolate-red, and others greenish-grey th< 

 rock passing by insensible transitions into ordinary unaltered shales 

 on the one-hand, and into silicious and micaeous slates on the other. 

 Many argillites are highly lustrous from intermixed graphite, and 

 some contain small straw-like crystals of chiastolite or andalusite, as 

 described under that mineral in Part II. Dark and more or less 

 lustrous varieties are common in Huronian strata, and are still more 

 abundant in the higher Animikie series of Thunder Bay, Lake 

 Superior (see Part V), and in various parts of the altered region 

 south of the St. Lawrence. In the latter district, as in Beauce and 

 elsewhere, many of the green, purplish, and red agillites present a 

 nacreous talcose aspect, but, as shewn by Dr. Hunt's analysis, they 

 contain little or no magnesia. 



Chlorite Slate : This metamorphic rock in its normal aspect is a 

 compound of chlorite and quartz, possessing a distinct green colour 

 and a foliated or schistose structure ; but in many examples the 

 structure becomes fine-granular or almost compact. Tn Canada, 

 chlorite slates, passing into chloritic strata in which the typical 

 character of the rock is more or less obscured, occur sparingly in the 

 Laurentian series, mostly in connection with iron ores. A bed of a 

 dark green colour, filled with numerous small octahedrons of mag- 

 netic iron ore, occurs in the township of Gal way. Other examples, 

 but often of -somewhat obscure schistose structure, are characteristic 

 of the Huronian rock throughout the vast region north of Lake 

 Huron and Lake Superior. In the crystalline region south of the St. 

 Lawrence, chloritic slates are also abundant, and most of the copper 

 ores of the Eastern Townships are associated with these strata. 

 Other beds contain intercalated scales and layers of specular or mica- 

 ceous iron ore ; and in the Townships of Bolton and Broughton, 

 more or less compact or subfoliated beds of greenish-grey chlorite, 

 known as " potstone," form workable beds of good quality. (See 

 Part II, No. 80). 



Steatite or Soapstone-Rock : This rock consists of granular or 

 slaty talc, frequently intermingled with carbonate of lime or dolo- 

 mite. It usually presents a greyish or greenish- white colour, and 

 when pure is very sectile. A bed of somewhat inferior quality, from 

 intermixture with calcareous matter, occurs in the Laurentian strata 

 of Elzevir. The closely related substance known as Pyrallolite (see 



