is to say, not greatly more than this period of time has
elapsed since it was in a molten condition. It may be as old as a
hundred million years, but its age is believed by those most competent
to judge to be more likely within this limit than beyond it. But if we
ask what is the thickness of the rocks which in past times have been
formed, and denuded, and re-formed, over and over again, we get an
answer, not in feet, but in miles. The Laurentian and Huronian rocks of
Canada constitute a stratum ten miles thick; and everywhere the rocks at
the base of our stratified system are of the most stupendous volume and
thickness.

It has always been a puzzle how known agents could have formed these
mighty masses, and the only solution offered by geologists was,
unlimited time. Given unlimited time, they could, of course, be formed,
no matter how slowly the process went on. But inasmuch as the time
allowable since the earth was cool enough for water to exist on it
except as steam is not by any means unlimited, it becomes necessary to
look for a far more powerful engine than any now existing; there must
have been some denuding agent in those remote ages--ages far more
distant from us than the Carboniferous period, far older than any forms
of life, fossil or otherwise, ages among the oldest known to geology--a
denuding agent must have then existed, far more powerful than any we now
know.

Such an agent it has been the privilege of astronomy and physics, within
the last ten years, to discover. To this discovery I now proceed to lead
up.

Our fundamental standard of time is the period of the earth's
rotation--the length of the day. The earth is our one standard clock:
all time is expressed in terms of it, and if it began to go wrong, or if
it did not go with perfect uniformity, it would seem a most difficult
thing to discover its error, and a most puzzling piece of knowledge to
utilize when found.

That it does not go much wrong is proved by the fact that we can
calculate back to past astronomical events--ancient eclipses and the
like--and we find that the record of their occurrence, as made by the
old magi of Chaldaea, is in very close accordance with the result of
calculation. One of these famous old eclipses was observed in Babylon
about thirty-six centuries ago, and the Chaldaean astronomers have put on
record the time of its occurrence. Modern astronomers have calculated
back when it should have occurred, and the observed t