450 ELEMENTARY GEOLOGY 
rate detail, beaches found every here and there show 
that the coast-line of the eastern margin of the in- 
terior sea stretched along the line now occupied by 
the eastern part of the Appalachians. This great 
series of Cambrian beaches extended from New Eng- 
land at least as far south as Georgia. 
There was apparently an extensive land area in 
Canada, and the site of some of the Archean moun- 
tains of the west was still occupied by land, though 
a part of this western region was beneath the sea. 
We know this because rocks formed in the ocean of 
that time have been found built into the mountains. 
From these facts it seems probable that the site of 
the Cordilleras was an archipelago, possibly like the 
East Indies of to-day. 
During this period the ancient eastern mountains 
were subjected to re-elevation; and from New KEng- 
land to Virginia, and probably further, volcanoes ex- 
isted, sending lava flows and ash eruptions to the 
surface. Volcanic rocks have also been found in 
the Cambrian of the Lake Superior district, so that 
we know that these two regions, now free from vol- 
canoes, were once the seat of active eruptions. 
The operation of the agencies of air and ocean seems to have 
been quite like that of the present, although it is possible that 
the air was still charged with different substances from those 
composing the atmosphere of to-day. Since much carbonic acid 
