372 CHAPTERS ON EVOLUTION. 



of the facts revealed by a study of the earth's life-history in the 

 past. 



The question of the general succession of life on the earth's 

 surface presents an important series of considerations to the evolu- 

 tionist's view. In this latter study, it is interesting to note the theory 

 of descent finds increased support. Admitting to the full the great 

 breaks which exist in the continuity of the rock-formations com- 

 prising the crust of the globe "blank periods " which in noway 

 militate against the correctness of evolution we still possess data of 

 sufficient accuracy and extent to determine for us the general order 

 in which life has been developed on the earth's surface. The further 

 back we pass in the history of the rock-formations, the fewer are the 

 resemblances we can detect to living animals and plants. Occasion- 

 ally we meet with certain forms which seem to have persisted from 

 the earliest times, and without material change, to the present day. 

 Such are certain of those shellfish named Brachiopods, and also many 

 of the Foraminifera. These have survived from a period so far back 

 as the Silurian epoch ; and appear before our eyes to-day as living 

 forms, in essentially the same guise as their fossil representatives. Such 

 examples of unaltering life have already been shown, in the chapter 

 on " Degeneration," to be perfectly consistent with the doctrine of 

 evolution. They represent species whose surroundings remain the 

 same to-day as of yore, and whose tendencies to change are, there- 

 fore, practically non-existent. A glance at the table of rock -forma- 

 tions already given (page 368) will show that time past has been 

 divided by the palaeontologist into three great periods, in so far as the 

 development of life is concerned. Thus the rocks from the Lauren- 

 tian, or oldest of the fossil-bearing series to the Permian are col- 

 lectively named "Palaeozoic" (or "Ancient Life") formations. 

 Those from the Trias to the Chalk form the "Mesozoic" (or "Middle 

 Life") period ; whilst the rocks from the Chalk to the soils of to-day 

 collectively form the " Kainozoic" (or "Recent Life") period. 



It is a matter of the most elementary study in geology to discover 

 that the fossil animals and plants of the Paleozoic period are most 

 unlike the existing life of the globe. The fossils of the Mesozoic 

 rocks approach more nearly in character to the animals and plants 

 around us, although also including many very divergent forms. In 

 the Kainozoic rocks ; on the other hand, we meet with a far larger 

 proportion of fossils belonging to living or " recent " species. 

 Broadly speaking, then, there has been a gradual development of life 

 from forms unlike those around us to-day, towards the existing life 

 of the globe. But geology goes much further in its interpretation of 

 the past life of our globe. There has been represented, in addition, 

 a distinct development of higher from lower life as the ages have 

 progressed. There have been progression and advance, as well as 



