SUCCESSION OF LIFE UPON THE GLOBE. 373 



the formation next above, than to that of any other series of 

 deposits. Upon no other view can we comprehend why the 

 Post-Tertiary Mammals of South America should consist prin- 

 cipally of Edentates, Llamas, Tapirs, Peccaries, Platyrhine 

 Monkeys, and other forms now characterising this continent ; 

 whilst those of Australia should be wholly referable to the 

 order of Marsupials. On no other view can we explain the 

 common occurrence of " intermediate " or " transitional " 

 forms of life, filling in the gaps between groups now widely 

 distinct. 



On the other hand, there are facts which point clearly to the 

 existence of some law other than that of evolution, and pro- 

 bably of a deeper and more far-reaching character. Upon no 

 theory of evolution can we find a satisfactory explanation for 

 the constant introduction throughout geological time of new 

 forms of life, which do not appear to have been preceded by 

 pre-existent allied types. The Graptolites and Trilobites have 

 no known predecessors, and leave no known successors. The 

 Insects appear suddenly in the Devonian, and the Arachnides 

 and Myriapods in the Carboniferous, under well-differentiated 

 and highly-speciahsed types. The Dibranchiate Cephalopods 

 appear with equal apparent suddenness in the older Mesozoic 

 deposits, and no known type of the Palaeozoic period can be 

 pointed to as a possible ancestor. The HippuritidcB of the 

 Cretaceous burst into a varied life to all appearance almost 

 immediately after their first introduction into existence. The 

 wonderful Dicotyledonous flora of the Upper Cretaceous 

 period similarly surprises us without any prophetic annuncia- 

 tion from the older Jurassic. 



INIany other instances could be given ; but enough has been 

 said to show that there is a good deal to .be said on both sides, 

 and that the problem is one environed with profound difficul- 

 ties. One point only seems now to be universally conceded, 

 and that is, that the record of life in past time is not interrupted 

 by gaps other than those due to the necessary imperfections of 

 the fossiliferous series, to the fact that many animals are in- 

 capable of preservation in a fossil condition, or to other causes 

 of a like nature. All those who are entitled to speak on this 

 head are agreed that the introduction of new and the destruc- 

 tion of old species have been slow and gradual processes, in no 

 sense of the term " catastrophistic." Most are also willing to 

 admit that " Evolution " has taken place in the past, to a 

 greater or less extent, and that a greater or less number of so- 

 called species of fossil animals are really the modified descend- 

 ants of pre-existent forms. How this process of evolution has 



