Pennsylvania Geology Final Report Volume 1 1981

6 GEOLOGICAL SIJRVEY OF PENNSYLVANIA.
explaining the comparative quietness, or the comparative
commotion of tlie age of each. Going backward in time
and downward through the rocks, he is compelled to give
time-names as well as mineral-names to the formations or
of beds which he describes. But his time-names
groups
can only be comparative, such as new and old, newer and
older, recent, ancient and archaic. Andihis mineral-names
also can only be : comparative uj)per, middle and lower.
These terms, however, can present no well-defined idea to
an}^ mind but that of a geologist, for they are the terms in
daily use among men for events which run their course in
a few days, or years, or centuries of human time, or for
things which are measurable by inches, yards or miles in the
country where those who use them live. A single one of
the principal rock formations of Pennsylvania required
more time for its deposit than the duration of the human
race from its first appearance on the planet until now. The
age of our primeval forest can hardly compare with the age
which one large coal bed reached before its life was destroj^ed
by the invasion of the overl jdng sands. If the limestone
dej^osits of the Cumberland valley could be measured not
by feet and yards but by years and centuries, and compared
with events of human history, we should merely get
a vague notion of enormous time, expressed by the old
phrase "a thousand years is as a single day."
Nevertheless, however ineffectual will prove the effort to
frame a clear idea of the whole course of geological time, or
even to define with any distinctness its major sub-divisions,
it is absolutely indispensable for the understanding of the
geology of any region to suspend our habitual estimates of
human events, and substitute for them the largest possible
conceptions of geological time, upon the grandest scale
which we are capable of imagining.
To the human individual who seldom lives beyond threescore
years and ten, and whose short life is crowded with
business affairs, time is considered a precious commodity to
be spent with economy, its loss and its waste lamented, and
its use converted into a religious duty.
But these ideas are products of the latest age of human
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