CHAPTEK YI. 
THE ERA OF ANCIENT LIFE. 
THE SILURIAN AND DEVONIAN AGES. 
As I have said, there is some evidence that the 
Archaean rocks were chiefly sedimentary, but they 
have been metamorphosed by the agencies already 
mentioned. If they were sedimentary in origin, all 
the known lands of the earth must have been under 
the dominion of the sea. Then the first chapter of 
the earth-book must have closed with the elevation of 
Archaean areas. 
Starting from Arcliaean areas, we may walk in 
almost any direction, particularly southward, and 
come upon a diflerent formation. The character of 
the rocks in most places shows that they belong to 
another period. We also discover in it distinct forms 
of life, both animal and vegetable. 
In some places this formation lies smoothly upon 
the Archaean strata, but in other places the older 
rocks were first very much eroded and irregularly 
grooved by water (Fig. 7). In other localities still 
they were tilted (Fig. 13) and considerably folded 
before the newer strata were deposited upon them. 
It is evident, then, that the newer strata would not 
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