passed. There are limestones abounding in fossils, with a
cosmopolitan life very wide spread to be recognized in every
continent, such as used to be known as the Trenton limestone,
the mountain limestone, the chalk. Perhaps every proper system
and period should be marked by such a limestone in the middle.
The time classed as late Permian and Triassic on the other hand
was one of uplift, disturbance, volcanic action and extreme
climates, which gave us the traps of Mt. Tom, the Palisades of
the Hudson, the bold scenery of the Bay of Fundy and the gypsum
and red beds which are generally supposed to be quite largely
formed beneath the air and beds of tillite formed beneath
glaciers. Then in the times succeeding, in many parts of the
world, degrading forces were more effective than uplifting so
that the mountains became lower, and the seas extended farther
over the continents. Then the prevalence of lime sediments was
so great that the "chalk" was thought to be characteristic
everywhere. And about the time the "chalk" the land was reduced
to a peneplain. A similar cycle may be traced from the
Keweenawan rocks to the group of limestones so widespread over
the North American continent and so full of fossils, which to
older geologists and oil drillers have been known, in a broad
way, as Trenton.

All this introduces a question--to which I wish to suggest an
answer--How is it that these cycles came to be? Were the outer
rock crust of the earth perfectly smooth the oceans would cover
it to the depths of thousands of feet and it is only by the
wrinkling of such a crust that any part of it appears above the
ocean. If the earth had a cool thin crust upon a hot fluid
interior, and that thin crust were able to sustain itself