Life Progressive. 409 
our existing continents and 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 zodlogy 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 paleontological 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 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 
