GENERAL OBSERVATIONS. 387 



vras formed. In the Devonian age the head of the gulf was still 

 farther to the northeast, — probably in the vicinity of Quebec, — and 

 opened southward over New England ; for coral reefs were growing 

 in the region of Lake Memphremagog during the earlier Devonian 

 ( P . 270). 



South of the eastern half of the St. Lawrence there appears to 

 have been a progress of the dry land southward, similar to that over 

 New York and the West ; for the Silurian and Devonian beds are 

 successively passed over in going towards New England. There is 

 reason for believing, as different geologists have urged, that the 

 granites and schists of the White Mountains were made of strata of 

 the Devonian age. Still farther south, beyond Worcester, in Mas- 

 sachusetts, and over Rhode Island, lay the Carboniferous marsh or 

 coal-making area of the New England basin ; while to the north- 

 east, over part of Nova Scotia and New Brunswick, there were the 

 far larger marshes of the Acadian basin : the two belong geographi- 

 cally to the same great region — then low — between the St. Law- 

 rence and the ocean, and probably had direct connection. 



After the Devonian, and the Subcarboniferous period in the next 

 age, the dry land expanded to nearly its present extent, and it be- 

 came covered with forests, jungles, and marshes of Carboniferous 

 vegetation. This condition oscillated with that of marine submer- 

 gence many times in the progress of the Coal period. But the dry 

 land appears to have reached a degree of permanence in the Appa- 

 lachian region after the Pittsburg Coal series, and, to a still wider 

 extent, throughout the whole interior eastof the Mississippi, after the 

 Upper Coal beds (p. 368), so that when the Carboniferous period 

 closed, the continent in this its eastern half was almost complete. 

 Over the whole surface, including New England, Canada, and the 

 British possessions eastward, no rocks occur between the Palaeozoic 

 and Cretaceous, excepting small strips of Mesozoic east of the Alle- 

 ghanies, and also in the Connecticut valley and Nova Scotia. 



The interior sea, which in Silurian and Devonian periods had 

 spread from the Gulf of Mexico over the whole Interior Continental 

 basin and stretched northward on the west side of the Azoic nu- 

 cleus to the Arctic, after many variations eastward and westward 

 in its extent through the whole Palaeozoic, was at last mostly limited 

 to the region west of the Mississippi, and the southern portion of 

 the Mississippi valley ; for here are located all the marine sediment- 

 ary deposits of the interior formed in later time. 



2. Mountains. — The mountains of the Palaeozoic continent were 

 mainly those of the Azoic, — the Adirondack, of northern New 

 York, other heights in British America, the Black Hills, and iso- 



