104 MODERN IDEAS OF EVOLUTION 



crumplings and foldings of the earth s crust, and we 

 know that this also is consistent with the operation 

 of law ; for it often happens that causes long and 

 quietly operating prepare for changes which may be 

 regarded as sudden and cataclysmic. 



3. Throughout the geological history there is pro 

 gress toward greater complexity and higher grade, 

 along with degradation and extinction. Though ex 

 perience shows that it may be quite possible that 

 new discoveries may enable us to trace some of the 

 higher forms of life farther back than we now find 

 them, yet there can be no question that in the pro 

 gress of geological time lower types have given place 

 to higher, less specialised to more specialised. Curi 

 ously enough, no evidence proves this more clearly 

 than that which relates to the degradation of old 

 forms. When, for example, the reptiles of the Meso- 

 zoic age were the lords of creation, there was appa 

 rently no place for the larger mammalia which appear 

 at the close of the reptile dynasty. So in the Palaeo 

 zoic, when trees of the cryptogamous type predomi 

 nated, there seems to have been no room in nature 

 for the forests of modern type which succeeded them. 

 Thus the earth at every period was fully peopled 

 with living beings at first with low and generalised 

 structures which attained their maxima at early stages 

 and then declined, and afterward with higher forms 

 which took the places of those that were passing 

 away. These latter, again, though their dominion 



