successive ages from below upwards in the order of their exposure. When
now he extends his explorations to another state like Utah or Wyoming, he
may find some but not all of the series exhibited in the Grand Cañon,
overlaid or underlaid by other strata which in their turn can be assigned
to definite places in the sequence. By the same method, the geologist
correlates and arranges the rocks not only of different parts of the same
state, or of neighboring states, but even those of widely separated parts
of North America and of different continents. But he learns that he must
refrain from over-hasty conclusions, for he soon finds that the
sedimentary rocks have not been constructed at the same rate in different
places during one and the same epoch, and that rocks formed even at one
period are not always identical in nature. But his guiding principle is
sensible and reasonable, and by employing it with due caution he provides
the palæontologist with the requisite knowledge for his special task,
which is to arrange the extinct animals whose remains are found as fossils
of various earth ages in the order of their succession in time.

CONDENSED TABLE OF PALAEONTOLOGICAL FACTS

__________________________________________________________________________
| | | |
YEARS | NUMBER OF | | | ORDER OF
NECESSARY FOR | FEET IN | GEOLOGICAL | GEOLOGICAL | APPEARANCE OF
FORMATION | THICKNESS | AGE | EPOCH | CHARACTERISTIC
| | | | GROUPS
______________|___________|______________|_______________|________________
| | | |
| | | | M B R A F I
| | | | a i e m i n b
| | | | m r p p s v r