INTRODUCTION. 3 



of fossil remains. From the beginning of the deposi- 

 tion of the stratified rocks it has been constantly 

 happening that animals and plants which have died 

 have been preserved in muds and sediments. These 

 sediments subsequently harden into rocks, and the 

 buried animals become fossils. From the fossils 

 thus buried we can get many glimpses of the life of 

 early times, and we have only to examine the fossils 

 preserved in the successive layers of rocks to be able 

 to formulate more or less of a detailed history of 

 the life of geological ages. 



Now this source of history has some decided 

 advantages. In the first place, when dealing with 

 fossils we are dealing with actual animals, and not 

 with a record simply. When we find a fossil we 

 know something of the size, shape, and appearance 

 of the actual animal or plant that once lived, and 

 thus we need not confine ourselves to general ideas 

 of type. We implicitly trust the evidence given us 

 by fossils, and do not have to ask if some modifying 

 circumstances have deceived us. When we find 

 a fossil oyster it is impossible to question that 

 oysters were in existence at the time of the deposi- 

 tion of the rocks in which the fossil was found, so 

 that the history drawn from this source is positive, 

 so far as it goes. 



But, on the other hand, although fossils give us 

 abundant details, the history which can be drawn 

 from them is sometimes nothing more than a history 

 of details, lacking in the perspective view that makes 

 up a true history. In the first place, taking all of 

 the layers of stratified rocks together, we do not by 



