20 Classification of Rocks, 



beds, wliicli decompose readily an exposure to the weather ; the Fucoides 

 partly retaiuing their form, and resembling small broken sticks or twigs. — 

 The formation rests upon the Potsdam Sandstone, and is seen along the 

 south shore of the Ottawa in many localities from Carillon to the Chatts, 

 At Grenville, and also at Aylmer, it occurs on both sides of the river ; from 

 the middle of the Allumettes Island it extends irregularly south to Prescott, 

 where it crosses the St. Lawrence into the United States. It should be 

 found also bordering the Potsdam Sandstone where this latter formation 

 crosses from Lake Champlain through Beauharnois to the north shore of 

 the Ottawa, above Montreal, thence it should form a baud running more or 

 less near to the north shore of the St. Lawrence to the neighbourhood of 

 Quebec. Its position west of Kingston would be along the south side of the 

 line of the Potsdam Sandstone, pointed out in the description of that forma- 

 tion. 



The Trenton Limestone. 



Tlie rock of this formation may, in general, be easily recognised — it is 

 almost always a pure, grey, blue, buff or blackish limestone, very regularly 

 stratified. Nearly all the good limestone in the inhabited portions of Ca- 

 nada East of Toronto, consists of this very important deposit. The lime- 

 stones West of Toronto belong to the Upper Silurian, while those used for 

 burning in the country occupied by the Laurentian rocks, are white, and 

 cannot be mistaken for the Trenton formation. Kingston, Ottawa, Mon- 

 treal, Quebec, and a great many of the towns and villages East of Toronto, 

 are built of materials derived from this rock. 



The Calciferous Sandrock is generally of a lighter colour, and mixed 

 with sand as its name denotes, although it contains some beds which resem- 

 ble the pure limestones of the Trenton series ; a little practice however will 

 enable the student of Geology in Canada to point out the difference. The 

 Trenton formation has been divided by the New York Geologists into four 

 sections, the Chazy, Birds Eye, Black Eiver, and Trenton Limestones, but 

 Mr. Logan considers them all united by their fossils into one. They repose 

 upon each other in the order above indicated, the Chazy being the lowest, 

 the Birds Eye resting on the Chazy, the Black Ptiver on the Birds Eye, and 

 the Trenton lying upon the Black Eiver. There are certain fossils jxiculiar 

 to each of those four divisions of the Trenton Limestone, while there are 

 others which prevail throughout the whole mass, and for the latter reason is 

 it considered to be a single formation. This rock is seen on the Eiver St. 

 Mary between Lakes Huron and Superior, on the Island of St. Joseph, and 

 again at the South-east end of the Georgian Bay ; from this latter locality^ 

 it runs eastwardly until it reaches the Eastern extremity of Lake Ontario,- 

 aud for some distance above Kingston. It is extensively spread out over 

 the country lying between the Ottawa and St. Lawrence, its western 

 limit in this region being the belts of Potsdam Sandstone and Calciferous 

 Sandrock above mentioned, as stretching from the neighbourhood of Pem- 

 broke, through Eenfrew, Lanark, Leeds and Grenville, to the St. Lawrence. 

 In Lower Canada it is largely developed in the neighbourhood of JMontrcal. 



