upper Silurian. 



Lower Silurian. 



1 8 Classification of Rocks, 



present purpose to have been the original surface of the earth. They con- 

 stituted the floor of the ocean upon which the Cambrian and Silurian rocks 

 were slowly deposited, and in our enumeration of these latter, we shall con- 

 sider the Laui-entions as the foundation supporting all the others. 



CANADIAN FORMATIONS. 



"We shall now proceed to the examination of the Canadian Formations 

 in detail, characterising each briefly, and concluding with a table of their 

 geographical distribution in the several counties of the province, so far as 

 this can be ascertained from the materials in our possession. Commencing 

 at the surface and proceeding downwards, the following is their order and 

 supposed thickness : — 



Devonian -! ^' Cl^^'-^^o and Portage Groups, 7,000 



( 2. Hamilton Group, .... .... 1,000 



3. Coruiferous Limestone,. ... 100 



4. Onondaga Salt Group, .... 350 



5. Niagara Limestones and Shales, 500 



6. Clinton Group, .... .... GO 



7. Medina Sandstone, 600 



8. Hudson River Group, 1,100 



9. Utica Slate, 100 



10. Trenton Limestone, ... 450 



11. Calciferous Saudrock, 250 



n h 'r,^ i ^2. Potsdam Sandstone,. . . 300- 



Lamonan. | ^3^ Huronian Rocks, 



14. Laureutian Rocks . 



Life- 



11,810 

 The thickness of the Laurentian rocks is unknown, and that of the 

 Huronian is stated by Mr. Logan at 10,000 feet. Deducting the Chemung 

 and Portage gToups, which are only to be found in Gaspe, in this Province, 

 we have for the fossiliferous rocks of Upper Canada the depth of 4,810 feet 

 or nearly a mile ; but it is probable that the Hamilton group does not attain 

 its full volume where it crosses the Western peninsula. The other measure- 

 ments taken principally from the works of the New York Geologists, are-, 

 probably not far from correct. 



The following are some further particulars concerning each of the fossili- 

 ferous formations of Canada : — 



Potsdam Sandstone. 

 This formation reposes in most places where it is seen in Canada, im- 

 mediately upon the Laurentian rocks, the only exception being near Lakes 

 Huron and Superior, where the Huronian lies between the Sandstone and 

 the older deposits. It takes its name from Potsdam, a town situated about 

 thirty miles from Ogdensburgh, in the State of New^ York. It is a sand- 

 stone sometimes very compact, almcst resembhng pure quartz, sometimes 

 fine and often coarse-grained, containing small rounded pebbles ; its colour 

 varies from white, yellowish or reddish, to bro"s^ii. At Potsdam it is very 

 regularly stratified, and splits readily into slabs of a convenient size for build- 



