

ARCILEAN TIME. 161 



have, never changed places with the oceans. Tracing out the develop- 

 ment of the American continent, from these Archaean beginnings, is 

 one of the main purposes of geological history. 



Source of the material of later fragmental rocks. — The Archaean 

 rocks, and rocks made from them, are the main source of the material 

 of subsequent non-calcareous fragmental rocks. Volcanic eruptions 

 have added a little to the supply ; chemical depositions also a little ; 

 and the siliceous secretions of the lowest orders of plants and animals 

 have contributed silica to some extent; but all these sources are small 

 compared with those of the Archaean terranes. From the fact pointed 

 out, that these most ancient of rocks were distributed, as the Silurian 

 era opened, in insular areas all along the Atlantic border — from Lab- 

 rador, through New England, southwestward (and other areas may 

 have existed, which are now at shallow depths under other rocks or the 

 sea-border) — it is seen, as Hunt has urged, that they were well situ- 

 ated for supplying, through the help of the ocean, mud, sand and gravel, 

 for the deposits that were in progress as the next era opened. And 

 their contributions have continued ever since to be used in rock mak- 

 ing, both directly and through the strata which had been made from 

 them. 



Life. — The earliest representatives of animal life on the earth had 

 no special organs, either of sense ; of motion, excepting minute hairs, 

 or hair-like processes ; or of nutrition, beyond, at the best, a mouth 

 and a stomach. It was life in its simplest or most elemental condi- 

 tion — systemless life — since neither of the four grand systems of' 

 the animal kingdom was distinctly indicated. Such was the beginning 



Indications of plants occur in earlier Archaean beds than those of 

 animals ; yet the absence of animal remains may be owing to the met 

 amorphism of the rocks. That plants preceded animal life on the 

 globe is altogether probable, because they may live and reproduce in 

 hotter waters ; and, therefore, a temperature admitting of the existence 

 of plants would have been reached, in the progressing refrigeration, 

 before that favorable to animal life. The fact, also, that animals need 

 plants for food (page 115), affords a strong presumption in favor oi 

 the view that plants were first in existence. 



