THE. BIOLOGICAL RELATIONS OF FOSSILS. 57 
CHAPTER WE 
THE BIOLOGICAL RELATIONS OF FOSSILS. 
Not only have fossils, as we have seen, a most important 
bearing upon the sciences of Geology and Physical Geography, 
but they have relations of the most complicated and weighty 
character with the numerous problems connected with the 
study of living beings, or in other words, with the science of 
Biology. ‘To such an extent is this the case, that no adequate 
comprehension of Zoology and Botany, in their modern 
form, is so much as possible without some acquaintance with 
the types of animals and plants which have passed away. 
There are also numerous speculative questions 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. ‘To 
discuss fully the biological relations of fossils would, there- 
fore, afford matter for a separate treatise ; and all that can be 
done here is to indicate very cursorily the principal points to 
which the attention of the palzontological student ought to 
be directed. 
In the first place, the great majority of fossil animals and 
plants are “ extinct”—that is to say, they belong to species 
which are no longer in existence at the present day. So far, 
however, from there being any truth in the old view that there 
were periodic destructions of all the living beings in existence 
upon the earth, followed by a corresponding number of new 
creations of animals and plants, the actual facts of the case show 
that the extinction of old forms and the introduction of new 
forms have been processes constantly going on throughout the 
whole of geological time. Every species seems to come into 
being at a certain definite point of time, and to finally dis- 
appear at another definite point; though there are few in- 
stances indeed, if there are any, in which our present know- 
ledge would permit us safely to fix with precision the times of 
entrance and exit. There are, moreover, marked differences 
in the actual time during which different species remained in 
existence, and therefore corresponding differences in their 
“vertical range,” or, in other words, in the actual amount and 
thickness of strata through which they present themselves as 
fossils. Some species are found to range through two or even 
three formations, and a few have an even more extended life. 
More commonly the species which begin in the commence- 
