DEVONIAN AGE. 287 



that there was some progress southward with each period. Nearly all 

 of Eastern Canada and New England was probably part of the dry 

 continent, from the close of the Lower Devonian, there being no Upper 

 Devonian or Carboniferous rocks over these regions, excepting in part 

 of Nova Scotia, and near the sea border of Canada, New Brunswick, 

 eastern Maine, and southeastern New England. 



The general map on page 144 shows the area over which the Si- 

 lurian and Devonian formations are now uncovered in other parts of 

 North America. We cannot positively conclude that no later rocks 

 •ever existed over these areas ; for extensive strata may have been 

 washed away in the course of subsequent changes. Yet the progress 

 of the emerged land southward, noted in New York, is apparent also 

 along the region of Ohio and Wisconsin ; and there was extension also 

 from the Archaean axis of the far north, westward and eastward : so 

 that a general expansion of the old Archaean land had taken place by 

 additions to all of its borders. South of New York, and over a large 

 part of the continent, the surface was still liable to alternate sinking 

 and rising, and was therefore open to new formations. 



North America was to a great extent a continental sea, with the 

 amount of land that was permanently dry very limited, as compared 

 with the present finished continent. In place of the Rocky Moun- 

 tains and Appalachians, there were only islands, reefs, and shallow 

 waters, marking their future site ; for Carboniferous strata and others 

 of later age cover the slopes of many of the Western mountains, and 

 a limestone of the Carboniferous age exists on them at a height of 

 13,000 feet above the sea. The Appalachians also contain, in their 

 structure, rocks of the Devonian and Carboniferous eras. The Green 

 Mountains were above the water, through the Devonian, but had only 

 part of their present height. 



It follows, from the limited area of the land and the absence of high 

 mountains, that there were no large rivers at the time. With the 

 close of the Devonian, the Hudson River may have existed with 

 nearly its present limits ; the Connecticut and some other New Eng- 

 land rivers may have begun their work ; and, in Canada, the Ottawa 

 and other streams drained the northern Archaean. Even the St. Law- 

 rence, above Montreal, may have been a fresh-water stream. 



3. Geographical changes. — The history of the periods of the De- 

 vonian has been shown to be, like that of the Silurian periods, a 

 history of successive oscillations in the continental level, — the posi- 

 tion of the accumulating deposits varying more to the east or to the 

 west with the varying location of the subsiding or emerging areas. 

 Throughout the whole, the Appalachian region continued to be well 

 defined. Its Devonian deposits consist mainly of shales and sand- 



