Life Progressive. 409 



our existing continents arid islands, fixed and immovable 

 as they appear, have been repeatedly sunk beneath the 

 ocean and just as repeatedly been lifted above its waters. 



Not only have fossils an important bearing upon geology 

 and physiography as has been seen, but they have relations, 

 most complicated and weighty in character, with the science 

 of biology, or the study of living beings. No adequate 

 understanding of zoology and botany is possible without 

 some acquaintance with the types of plants and animals that 

 have passed away, for there are numerous speculative prob- 

 lems in the domain of vital science, which, if soluble at all, 

 can only hope to find their key in researches carried out on 

 extinct organisms. 



No attempt will be made by the writer to discuss fully the 

 biological relations of fossils. Such an undertaking would 

 afford matter for a separate volume. All that I purpose in 

 this chapter is to indicate very cursorily the principal points 

 of palaeontological teaching, so that my readers can acquire 

 some idea of the progression from lower to higher types 

 that life has made throughout the geological ages. Prelimi- 

 nary to the purpose held in view, let it be understood that 

 the vast majority of fossil animals and plants are extinct, or, 

 differently and perhaps more intelligently expressed, belong 

 to species that no longer exist. So far from there being any 

 truth in the old idea that there have been periodic destruc- 

 tions of all the living beings in existence upon the earth, 

 followed by a corresponding number of new creations of 

 plants and animals, the actual facts indicate that the extinction 

 of old and introduction of new forms have been processes 

 that have been continually going on throughout the whole 

 of v geologic time. . Every species seems to come into exist- 

 ence at a definite point of time, and to disappear finally at 

 another definite period, though there are few, if any, instances, 

 in which the times of entrance and exit could be fixed with 

 any degree of certainty or precision. Marked differences in 

 the actual time during which different species have remained 



