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Irish deer, the mammoth, mastodon, woolly-haired rhino- 

 ceros, and other animals long since extinct, we feel assured 

 that vast changes in physical geography have taken place 

 since their entombment, and are entitled to assign to them 

 a still higher antiquity. In fact we know that all changes 

 in physical conditions, and all removals and extinctions 

 of life, take place by slow and silent stages, and that the 

 greater the diiference between the existing and the extinct, 

 the longer must be the time that has elapsed since their 

 extinction. By methods such as these we can establish a 

 scale of old, older, oldest ; and there need be no more un- 

 certainty about the results obtained by such methods than 

 there is about the results obtained by the historian in 

 modern, medieval, and ancient history. 



Another method by which we arrive at notions of relative 

 antiquity is by the implements and works of art that occur 

 in recent formations, or accompany the remains of man. 

 "We know the phases of modern, medieval, Eoman, Greek, 

 Egyptian, and Babylonian art, and can assign something 

 like a historical date to such objects and the accumulations 

 in which they occur. We know, too, that man employs tools 

 of wood and stone long before he learns the uses of the 

 metals; and that he reduces the softer metals, and works in 

 copper and bronze, long before he has acquired the mastery 

 over iron and steeL In this way we speak of the ages of 

 stone, bronze, and iron, the one preceding the other, and 

 forming, as it were, a rude scale of time for the antiquarian 

 and geologist But while one nation may be working in 

 iron, another more belated may be working in bronze, and 

 a third, still more remote and savage, may be adhering to 

 implements of wood and stone. To be of any use, this 

 scale of stone, bronze, and iron, must be applied to the same 

 district; and when so applied, archaeologists are now pretty 

 well agreed that it marks with considerable certainty the 



