OF CENTRAL CANADA PART II. 12T 



make tip the strata of the Guelph Formation, as seen in the Town- 

 ships of Elora, Guelph, Dumfries, Waterloo, Bentick, <fcc. ; and dolo- 

 mitic limestones, or mixtures of limestone and dolomite, belong to 

 the various other formations of this series, more especially to Cal- 

 ciferous, Chazy, Niagara, and Onondaga strata, as described under 

 these divisions in Part Y. 



91. Magnesite : White, brownish, &c. Hemi-Hexagonal in crys- 

 tallization, the crystals mostly obtuse rhombohedrons ; but occurring 

 commonly in cleavable masses (with cleavage angles = 107 29' and 

 72 31')' and in granular and rock varieties. H (in pure varieties) 

 = 3.5 4.5 ; sp. gr 2.8 3.0, or slightly higher in the brown fer- 

 ruginous varieties. BB, infusible. Soluble in heated acids with 

 effervescence. Normal composition : carbonic acid 52.4, magnesia 

 47.fi, but part of the magnesia usually replaced by protoxides of iron 

 and manganese. In Canada, this mineral occurs only in rock masses? 

 forming beds in the altered strata of the Eastern Townships of Sut- 

 ton and Bolton, south of the St. Lawrence, where it is associated 

 chiefly with serpentine and steatite. 



92. Rhodochrosite, or Carbonate of Manganese : This species has 

 not yet been found in Canada in distinct examples, but it occurs in 

 admixture with many of the manganese ochres (No. 96), and is also 

 present, in traces, in some of the altered strata of the Eastern Town- 

 ships. Colour, rose-red or pale-red, weathering brown. 



93. Siderite or Spathic Iron Ore (Spherosiderite, Clay Iron Ore, 

 <fe c .) : Yellowish, greyish, light and dark brown, green, &c. Occurs 

 under several conditions, and more especially: (1), in rhombohe- 

 drons, scalenohedrons, and lamellar masses, with cleavage angles of 

 107 and 73 (Spathic Iron, proper); (2), in spherical or concre- 

 tionary masses with radiating fibrous structure in trappean rocks 

 (Spherosiderite) ; and (3), in nodular masses and occasionally in 

 layers, mostly of a brown colour and earthy or dull stone-like aspect 

 (Clay Iron Ore). Crystalline varieties of this mineral have not yet 

 been recognized with certainty in Canada; but nodules and thin 

 layers of clay ironstone or clay iron ore occur in the Devonian strata 

 of Gaspe, associated with a small seam of impure coal, and with fos- 

 silized plant-remains. This variety is a mixture of carbonate of iron 

 (more or less converted into brown iron ore) with argillaceous mat- 



