80 Ti^AXSAcrioxs of the Ameeican Ixstitute. 



of the strata is the result of a subsequent operation ; and "svlierever it 

 takes place it weakens the beds, so that they are more frequently 

 eroded along the line of folding than elsewhere. It is to be kept in 

 view that the materials out of which the rocks of the continent are 

 composed have been distributed over the bed of an ocean. They con- 

 sist of materials transported from pre-existing continents or islands, 

 which are carried into the ocean and spread out over its bed. 



Before speaking of the history of the continent, I will point out 

 the divisions by this chart. This color represents the earliest known 

 portion of the continent, composed of sedimentary deposits. TVe 

 know of no other rocks except those which have been deposited from 

 water, except in very limited areas. All the materials which com- 

 pose in any great degree the North American continent have been 

 deposited from water in the form of sand, clay, and limestone ; the 

 limestone being originally in the condition of fine mud or a calcareous 

 sand. We have in these rocks the evidence of this condition in the 

 shape of corals, which can only exist in a quiet ocean. "VVe have here 

 shells similar to those in our modern oceans, and of a character 

 showing that they have lived, not in the deep sea, but along the shore 

 line. 



It has only been within a comparatively few years that we have 

 come to a knowledge of the fact that the northern portion of the 

 American continent is formed of stratified sedimentary rocks. All 

 this granite region of the country, stretching along the St. Lawrence, 

 occupying a great portion of Canada, reaching towards Hudson's Bay, 

 and extending southward into the northern part of New York, is 

 composed of nothing more nor less than sedimentary rocks, deposited 

 as sand or carbonate of lime, having subsequently undergone the 

 change we call metamorphism. This older granitic portion of the 

 country — granitic because its materials are of coarse, crystalline matter, 

 of which I have specimens here before you, is essentially embraced 

 within this northern portion of the continent colored red upon the map. 

 This formation, known as the Laurentian System, has an enormous 

 thickness, composed of beds of gneiss, crystalline limestones, Labra- 

 dorite, or felspathic granite, together with gneissoid or sienitic con- 

 glomerates in some parts of its extent, which, as a whole, has resulted 

 from the sediments deposited in this primeval ocean through countless 

 ages. All this had been accomplished before there was any spot of 

 land to which we can point as constituting part of the American 

 continent, and where all that area which I now present to you upon 



