THE RECORD FROM FOSSILS. 93 



change that took* place in animal life, they must 

 have been at least as long. Owing to these lost 

 records it frequently happens that the opening of 

 the different periods shows a surprising acquisition 

 of the new forms of life. The sudden appearance of 

 new types of life at the opening of the Tertiary (9), 

 for example, is doubtless due to the fact that we do 

 not possess the history of the immediately preceding 

 period ; and so also the sudden appearance of life 

 with the Silurian (2) is in the same way due to the 

 absence of any record of pre-Silurian life. 



Life at the Beginning of the Fossiliferous Record. 



We will now turn our attention more closely to the 

 development of life during these ages. In the first 

 place it must be noticed again that it is no longer 

 possible to trace the history of life along a single 

 road. The Gastraea was the last point which the 

 various types of animal life had in common. From 

 this point many of the types diverged, and the com- 

 plete study of the history of life would lead us to 

 follow each of them. This would, however, involve 

 a mass of detailed statistics which would be largely 

 unintelligible to the general reader. Instead of fol- 

 lowing the history of life through its numerous de- 

 tails, we shall try therefore to take a perspective 

 view of it ; noting the general truths and laws illus- 

 trated by the course of development. 



Let us retrace our steps, and study more carefully 

 the history of life during the geological ages. First 

 we may ask, What was the condition of the animal 

 kingdom at the time of our first fossil record of it ? 



