Animals Before Man 



they might be carried from one region to 

 another. 



To apply these facts to the history of our 

 own country, it may be said that fishes still liv- 

 ing hint at a former union between North 

 America, Asia, and Europe, while the testimony 

 of fossil mammals is to the eifect that Europe 

 and this continent were united just before, or 

 during, the Eocene period. Fossil elephants 

 and mastodons speak of an early connection 

 between Asia and America, while existing ani- 

 mals show that very recently (geologically 

 speaking) Alaska and Siberia were connected 

 by a land bridge in the vicinity of Bering 

 Straits. 



As for the testimony of the rocks them- 

 selves, thick beds tell of long periods of quiet, 

 when changes in the earth's crust were few and 

 slow, while thin beds of rock speak of fre(j[uent 

 changes of level. Fine-grained limestones in- 

 dicate the presence of lime-secreting creatures 

 such as corals and crinoids, or perhaps of those 

 stony-jointed plants, the so-called nullij^ores, 

 once counted with the corals, and, like them, 



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