Page:Walcott Cambrian Geology and Paleontology II.djvu/30

Theoretical profile of North American continent on line of Forty-eighth parallel, during part of Algonkian time. The Cordilleran, Superior, St. Lawrence, and Newfoundland epicontinental Algonkian scas are assumed to have been shut off from communication with the oceans during Algonkia time, except an occasional and very brief connection of the Cordilleran lakes with the Pacific Ocean.

Fig. 1.