536 



HISTORICAL GEOLOGY. 



region of Wisconsin, on the borders of New York and Canada, and about the 

 Adirondacks. The Taconic Kange had just been made, and probably a 

 Taconic system, consisting of ranges from Canada to Georgia ; and as a part 

 of the uplifting, the eastern portion of New York became emerged, and also 

 a large area along the Atlantic, south of New York. (The Archaean limits 

 in the latter area are not marked, because not yet defined.) Western North 

 America was not notably changed. 



The upward movements, moreover, closed against the sea the broad St. 

 Lawrence channel. This channel had been in earlier time a great highway 



737. 



North America at the opening of the Upper Silurian. 



for tides and currents, and what they could transport between the Atlantic 

 and the Continental Interior. But now the Interior Sea had to depend for 

 rock-making material on what could be gathered from its borders and the 

 stony secretions of aquatic life. But it left open the northeastern troughs, 

 east of the Green Mountains and St. Lawrence — the Connecticut valley 

 trough, the Gaspe- Worcester, and the Acadian, or that from western New- 

 foiindland to Narragansett Bay, over the Bay of Fundy and Massachusetts 

 Bay; for these have severally their Upper Silurian and later rock forma- 

 tions. It is even probable that the Gaspe-Worcester trough had its eastern 

 Archaean confine, which separated it from the Acadian trough, extended 



