20 INTRODUCTION. 



as yet we can only dimly picture : that there is a succes- 

 sion in the forms of life, as we ascend the geological scale. 

 Higher and higher organisms appear, and yet the lower 

 forms, although generally much modified, remain ; while 

 also the very lowest types continue to exist, and range 

 through vast intervals of time, sometimes with but little 

 variation. Different forms were suited to the ever-varying 

 physical conditions. As these conditions altered, some 

 species died out, and others migrated to more favourable 

 areas, to be replaced by new forms ; while those species re- 

 mained which were fitted to endure the change. Varieties 

 may thus have profited largely by the altered circumstances, 

 and would doubtless be perpetuated and multiplied, well illus- 

 trating the doctrine which teaches the ' survival of the fittest 

 in the struggle for existence.' Not the least interesting part 

 of Geology is the light thrown on the present geographical 

 distribution of plants and animals, by a study of the physical 

 changes which the earth's surface has undergone in past times.^ 

 The study of Fossils, or Palaeontology, is thus intimately 

 connected with Zoology and Botany, for the recent forms 

 enable us to judge what were the habits of the extinct, while 

 only by a study of the fossil forms can we expect to explain 

 the origin or development of the living. 



In interpreting the climates of the past from the organic 

 remains found in the strata, we must of course be cautious 

 in considering that the genera were adapted to the same 

 climates in which they now flourish, for the variations of 

 species may have enabled them to endure different climates. 

 Until the woolly-haired Elephant and Rhinoceros were found 

 embedded in the ice of Siberia, we had no notion that animals 

 of their kind could withstand the rigours of an arctic climate. 

 And as only the bones and shells and other hard parts of 

 animals are, as a rule, preserved to us in the rocks, we can- 

 not always safely assume that they were adapted to precisely 

 the same conditions as their modern representatives. But of 

 course we have also the evidence of plant-remains, and when 

 we find associated, forms of life whose modern representatives 

 co-exist only under certain conditions, the inferences that 

 may be drawn are fair and legitimate, even if not in all cases 

 absolutely conclusive. 



Climate is the result of influences that belong to the world 

 in general, even to the Solar system. And we know, by 



- Darwin, ' Origin of Species ' ; A. R. Wallace, Geographical Distribution of 

 Animals ; J. Phillips, Life on the Earth, i860. 



