SUMMARY. 117 



veloped, so well fitted its place in nature that further 

 change would be unnecessary, unless some change in 

 conditions should arise. This is, however, only a 

 suggestion, not an explanation. 



Summary. 



"It must be conceded that, on the whole, the 

 testimony of the rocks is in favor of the doc- 

 trine of evolution," is the decision of the most 

 advanced geologists to-day. Undoubtedly there 

 are many difficulties in the way, and very seri- 

 ous some of them are, which yet remain unan- 

 swered. The sudden appearance of such a highly 

 differentiated fauna at the very base of the Silurian, 

 and the character of this fauna, consisting, as it did, 

 of all of the sub-kingdoms, are facts which are 

 unfortunate for the evolution theory ; for, if they 

 do nothing else, they make it utterly impossible to 

 show that the great types are related to each other 

 by converging lines. The absence of life in rocks 

 older than the Silurian, shrouds in absolute darkness 

 the origin of the various sub-kingdoms and classes, 

 for at the very first glimpse we have of life they 

 were as widely apart as they are now. The result 

 of careful research, which tends to show that a very 

 large majority of our orders, sub-orders and families 

 can be traced back to these early times, makes it 

 still more difficult to recognize converging lines, and 

 confines the search chiefly to the one group of ver- 

 tebrates which has developed since that time. The 

 occasional survival of some forms almost unmodi- 

 fied through the enormous geological ages ; the great 



