OF CENTRAL CANADA PART II. 125 



good polish. They are mostly of a brownish-yellow color. Caverns 

 and hollows of greater or less extent often occur in limestone recks. 

 Water percolating into these through minute fissures in the roof, 

 very generally deposits on the latter a thin coating of carbonate of 

 lime, and then dropping on the floor, deposits there a further portion 

 of calcareous matter. In this manner, the process constantly going 

 on, stalactites and stalagmites originate, the two occasionally meet- 

 ing in the form of a pillar (as shown in Figure 76). These stalacti- 

 tic deposits usually exhibit a radiated fibrous structure, with fre- 

 quently a botryoidal surface. Some large stalactites have been 

 obtained from a cavern at the lower falls of the Nottawa River in 

 Mono (Geological Report, 1863, p. 334) ; and others, of smaller 

 size and less symmetrical form, have been found in adjoining town- 



(c) Rock Varieties : These come properly under review in Parts 

 III. and Y. of this work. They comprise the various kinds of lime- 

 stone, including : Crystalline Limestone, the finer varieties of which 

 are commonly known as Marble ; Ordinary Limestone ; Lithographic 

 Limestone ; Oolitic Limestone, composed of minute spherical con- 

 cretions ; Earthy Limestone or Chalk, and so forth. In Canada, 

 valuable beds of marble occur in the Laurentian strata of Renfrew 

 (Arnprior), McNabb, Grenville, Weiitworth, Bastard, Marmora, 

 Elzevir, &c. ; and in the metamorphic region south of the St. Law- 

 rence, as in St. Armand, St. Joseph, Melbourne, Oribrd, Dudswell 

 and elsewhere, many of the marbles from these localities being mixed 

 with green and other coloured serpentine. In some of the unaltered 

 Lower Silurian strata, also, red, grey, black and brown marbles 

 occur; as at St. Lin, Caughnawaga, St. Dominique, Montreal, Corn- 

 wall, Point Clare and Pakenham. See further, under Part V. 



89. Arragonite (Prismatic Carbonate of Lime) : Colourless, and 

 of various colours yellow, blueish, brownish-red, &c. Rhombic in 

 crystallization, and often in compound crystals which sometimes 

 present a pseudo-hexagonal aspect. Also in fibrous and stalactitic 

 masses. H = 3.5 4.0; sp. gr. 2.9 2.95. BB, infusible, but 

 becomes opaqu > and falls into powder. Soluble in acids with strong 

 effervescence. Composition identical with that of calcite : carbonate 

 of lime being thus a dimorphous body i.e,, a substance capable of 

 .assuming two distinct sets of physical characters. Fibrous arragonite 



