INTRODUCTION 



tion of these can ever be accessible to discovery. Then 

 we begin to realize that the display cases before us 

 contain all the organic beings which have been pre- 

 served from those which peopled a continent during 

 millions of years. This bone is the sole relic of many 

 genera of animals; and this handful of shells is the 

 recovered remnant of the countless life of the sea dur- 

 ing other millions of years. From what we have col- 

 lected from the past and from observation of forms 

 at present alive, a theory of evolution has been labo- 

 riously developed which explains our existing life as 

 the result of a continuous modification of previous 

 forms, going back to simpler and simpler organisms 

 until we reach a world of inorganic matter with here 

 and there tiny masses of protoplasmic jelly scattered 

 on the shores of the ocean, themselves indistinguish- 

 able from the mud in which they lie. 



Yet from these few and wholly inadequate facts, 

 the history of the world, from the time when it was a 

 molten and fiery mass to the present time, is given to 

 us by geologists and biologists. The changing struc- 

 ture of land and sea is traced ; the succession of plants 

 and animals is outlined, not in vague and general 

 terms, but specifically from type to type; a table of 

 time is worked out which, although it may vary in 

 details of a million years here and there, is neverthe- 

 less agreed upon in its main groups. The ages of rock 

 strata and of mountains and seas are specified, and the 

 changes coincident in organic life are noted. Not only 



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