ARCHEAN AND PALEOZOIC GEOGRAPHY 449 
The eastern land was also a mountainous one, with 
chains extending approximately parallel with those of 
the present Appalachian chains; but this mountain 
range was east of the Appalachians, and their site 
was then covered by water. Before the beginning 
of the Cambrian, the ancient eastern mountains, which 
had once risen into the form of extremely lofty ranges, 
were worn down to a series of hills, not unlike those 
of New England. Again and again, in later times, 
mountain folding has occurred in this eastern range, 
and between the times of folding there were periods 
of destruction by denudation. 
Cambrian Geography. — Although we are able to 
form a somewhat clearer idea of the physical geog- 
raphy of this period than we were of the Archean, 
our knowledge of it is nevertheless very limited. 
We are able to say very little about the climate of 
the Cambrian, for the life record that has been found 
is that of ocean animals, which give us no clue con- 
cerning the conditions upon the land. 
For a time, and possibly throughout the entire 
period, the site of the great Mississippi valley was 
occupied by the sea; and so it remained throughout 
nearly the entire Paleozoic era. The Adirondacks 
rose as an island in this ocean, and the ancient Cam- 
brian beaches are now revealed at their base. While 
it is not possible to trace the old shore-line in accu- 
2G 
