96 MINERALS AND GEOLOGY 



bearing series of Thunder Bay, Lake Superior, and abundantly in 

 imbedded nodular masses, and in thin layers in the Corniferous 

 Formation of the Devonian series of Western Canada, on the shore 

 of Lake Erie, &c. ; as well as occasionally under similar conditions 

 in limestones of the Niagara and Trenton groups. Hornstone, or 

 related silicious matter, forms the fossilizing substance of most of 

 the corals and brachipods of our Western Devonian beds, as well as 

 that of many of the organic remains found in Silurian strata, as at 

 Pauquette's Rapids on the Ottawa, and elsewhere. 



(h) Sandstones ; Sands ; Gravel : Sandstones consist essentially 

 of quartz grains, cemented together, or consolidated by pressure (see 

 Part III) ; whilst sands and gravel consist of the same substance in 

 loose grains and pebbles. These rock matters, although occasionally 

 colourless, usually exhibit various shades of yellow, brown, or red, 

 from the presence of sesquioxide of iron. Sandstones are also 

 occasionally of a green or greyish-green colour, in which case part 

 of the iron is in the condition of protoxide. Some of our purest 

 sandstones and quartz sands are found at the following localities : 

 Pittsburg township (near Kingston) ; Charleston Lake, in Escott ; 

 Vaudretiil, on the Lower Ottawa ; Beauharnois ; the Gres Rapids, 

 on the St. Maurice ; Township of Batiscan ; and also near Brock- 

 ville, Perth, Owen Sound, Dundas, &c. (see Part Y.) 

 (2) GROUP OF BASIC SILICATES. 



[This group includes a small number of silicates in which the per- 

 centage of silica varies from 30 to 40. The specific gravity is com- 

 paratively high (=3.0 to 4.75) ; and the hardness sufficient in all 

 cases to scratch glass strongly (=5.5 to 7.5, but mostly over 6.0)]. 



44. Zircon : Brown, red, reddish-yellow, with resino-vitreous 

 aspect. In Tegragonal crystals, mostly square prisms, termiuated at 

 each extremity by a four- planed pyramid 

 (Figs. 54, 55) ; occasionally also in small 

 granular masses. H = 7.5 . sp. gr. 4.0 - 

 4.75. BB, quite infusible. Not attacked by 

 acids. Consists of: silica 33.2, zirconia 66.8. 

 Occurs with plumbago, wollastonite, pyroxene, FIG. 54. FIG. 55. 



<kc., in the crystalline limestone of the Township of Grenville, in 

 Argenteuil County, and more or less throughout the phosphate 

 deposits of Buckingham, Templeton, <fec., often in fine crystals. 



