8 The Value of Paleontology. 
The original question, the exactitude of the chronological sig- 
nificance of structural types, has been momentarily held in abey- 
ance. Is paleontology a science so far exact as to furnish a 
chronological scale of terrestrial strata? The admission that the 
known tertiary faunz, for instance, are but fragments of a con- 
tinuous succession, would appear to invalidate any such claim. 
It would indicate that the restriction of a given type to a given 
horizon is only a matter of discovery, and that another accident 
may at any time give it a new range. This objection has but 
little weight. Fragments though they be, nearly related forma- 
tions as the Tertiaries, are obviously the visible portions of a serial 
succession of life. Like the bright lines in a spectrum, the order 
is not disturbed by the temporary obliteration of a part of the 
colors, but the visible portions indicate the relations of the com- 
ponent parts with infallible certainty. The more universal the 
physical interruption, the more far-reaching the break in the suc- 
cession of life in any one locality, and hence the greater the value 
of remains of animals as indication of relation in time. The 
change of faunz in Arctogzea at the close of the cretaceous is a 
case in point. A dinosaur, sauropterygian, ammonite or rudist 
are as definite indicators of the life that preceded the change as a 
tapir or civet-like carnivore is of the age that followed. 
It has been stated that the life of the present period in the 
Southern Hemisphere is not homogeneous. The same is true 
in a still smaller degree of the Northern. Thus, if we 
include India in the latter, the, elephant is a miocene form, and 
the true rhinoceros pliocene. Further north, the dogs are mio- 
cene. In North America the opossum, and probably the raccoon, 
are eocene; the wolves and foxes are miocene, and the weasels 
pliocene. Perhaps the cats first appeared in our pliocene. Com- 
paratively few mammalian types mark the latest geologic epochs. 
Such are the ruminants, as deer, antelope and oxen, with the true 
horses, which all commence in the upper pliocene of Europe. 
Finally, man alone signalizes the last or glacial period, and is to 
reach his culmination in the ages that intervene between that 
great time boundary and one to come. 
Thus a certain proportion only of the life of a given epoch is 
characteristic of it, that is, originates in it, the remaining mem- 
bers: being legacies from preceding ages. E. D. Cope. 
