CHAPTER XIV 

 THE ORDOVICIAN PERIOD 



Expansion of the sea in North America. By the end of 



the Cambrian period the sea had overspread the greater part 

 of North America. Neglecting certain retreats and read- 

 vances of this sea, the salient fact is that the general submer- 

 gence seems to have been greatest during the Ordovician 

 period (Fig. 339), gradually giving place to the reverse tend- 

 ency toward the close. On the east side of the continental 

 sea lay the island of Appalachia, an extensive land stretching 

 from New England to the Gulf states entirely east of the 

 present Appalachian ranges. Westward from this island an 

 open sea spread over the interior of the continent, probably 

 joining the Pacific. Some interrupting islands, whose out- 

 lines are imperfectly known, are thought to have existed in 

 the western part of the country. On the north lay other 

 lands now represented by the ancient rocks of eastern Canada 

 and adjacent parts of the United States. That much of this 

 sea was shallow is indicated by the remains of corals of the 

 reef-making type and other animals which to-day are unable 

 to live in deep water. Such a shallow body of salt water 

 lapping up over the continent is termed an epicontinental sea. 

 Many single species of Ordovician fossils are found alike in 

 Europe and in the United States, a fact which seems to mean 

 that it was possible for the animals of the shallow waters to mi- 

 grate freely from one continent to the other. As some of these 

 animals find it almost as difficult to cross the deep parts of 

 the ocean as to pass a barrier of dry land, we may suppose 

 that the shallow sea which spread over parts of Canada was 

 directly connected with the similar sea of northern. Europe. 



339 



