1856.] Prof. Rogen^on the Geology of North America. 167 



WEEKLY EVENING MEETING, 

 Friday, February 8. 



Sir Henry Holland, Bart. M.D. F.R.S. Vice-President, 

 in the Chair. 



Professor Henry D. Rogers, 

 (From the United States,) 



On the Geology and Physical Geography of North America, 



The speaker stated that his object in this discourse was to present 

 a condensed view of the physical features and geological outlines of 

 North America, — a country highly interesting, from the majestic 

 scale of its natural structure — from its peculiar position on the 

 earth's surface, lying intermediate between Europe on the one 

 hand, and Asia and Australasia on the other — as a half-way house 

 to connect the commerce and civilization of the world ; and tenanted 

 by an energetic people, essentially a composite nation, made up of 

 the enterprising and ardent spirits, who have gone from the various 

 more civilized countries of Europe. 



Taking a comprehensive but rapid survey of the general physical 

 features of North America, we find it presents but two great slopes, 

 one sinking towards the Atlantic, the other towards the Pacific, 

 divided by a lofty mountain axis, the Chippewayan or Rocky Moun- 

 tain chain, the true watershed or backbone of the continent. 



From either base of this chain, where the plain of the country 

 has an elevation of 5000 to 6000 feet above the sea, the continent 

 slopes eastward and westward, interrupted by only two important 

 intervening mountain swells— the Atlantic or Appalachian chain, 

 and the Pacific or Californian. These oceanic chains only partially 

 turn the drainage ; some of the largest rivers, the Susquehanna and 

 Kanawha, in the one case, Frazer's River and the Great Columbia in 

 the other, cutting quite through them. Another broad swell of the 

 surface crosses the continent, nearly westward, from Labrador to the 

 sources of the Columbia, passing between the Lawrentian Lakes and 

 Hudson's Bay, and between the sources of the Missouri and those of 

 the Saskatchawan. From this the continent slopes gently north- 

 wards, to its Arctic shores, and southwards, to its Mexican. All 

 these slopes are well indicated in the river drainage. 



Looking closer, there appear seven grand primary divisions of 



