The morning call. [volume] (San Francisco [Calif.]) 1878-1895, 1893-11-12
THE MEASURE OF PAST ACES.

Professor Prestwitch. the well-known sa-
want, has called halt in the knotty spec
ulations of modern physicists on the rate
at which changes are taking place in the
surface of the earth. Some biologists take
note of the rate at which the surface rises
or falls at the presentday. and assume that
the same rate prevailed throughout geo.
logical history; hence they undertake to
tell US how long it took to lift the CONT
nents now inhabited to their present level.
For instance. the coasts of Norway and
Sweden are known to be rising at the rate
of two and half feet in century. and
North Cape at the rate of five feet, while
the coast Of Greenland is subsidiDg at
rate which has caused gardens that were
cultivated in the seventeenth century to be
covered by the tides to-day. On this GER
tain scientists have evolved formula
specifying the rate which the surface OF
the earth rises or falls. Yet it is evident
that the causes which produce such move
ments must vary in power with the vary
ing stress to which the crust is exposed
from time to time and consequently that
their rate of progress Ia not uniform, but.
on the contrary, highly variable. SUCH
measurements as two and half feet In
century fail TO account for the sinking OF
the town at the mouth of the Indus or for
the discovery, in strata of clay far beneath
the surface, of gold ornaments on the
coast of South America.
So again with speculations on the length
Of the period which has elapsed since the
world first became habitable. Calculations
have been made on the number of years
required to cool a known spot which at
one time was in q state of igneous incan-
descence. and on the product, one school of
physicists have decided that the world
must have been Inhabited for a million
years, while another holds that twenty
million years are none too many to allo W
for the period. Such speculations pos
sess little scientific value, because we have
no means of knowing how fast or how
slow geological changes proceeded in former
ages. Men of science have figured exactly
how many years it takes to-day for 10 inch
of gravel to accumulate by river drift.
and they have hence tried to reckon how
manv centuries have passed since the bones
of the driftmen were deposited But the
estimate assumes that the force of the drift
was always The same as it is to-day, which
is quite unlikely.
Until science takes larger sweep we
must be content with knowing that the
world has passed through various changes
in which its shape, its climate and its
elevation have been very different from
what they are now. We are absolutely
without inform alton as to the length of
time which these various stages occupied.
We cannot even tell how long it took to
convert a tropical forest into bed of
bitnmin Gus coal. But we are learning !;
the limit of geologica knowledge at the
close Of the last century demonstrates how
fast. If our posterlty learn as fast as re-
cent generations have learned professors
may be able at the close of the twentieth
century to form shrewd guess at the
number of centuries which divide US from
the man Of the auarternarv period.