erosion.

Far more material than could have been washed down the slopes of the
first land ridges came directly from the interior of the earth, and
spread out in vast, submarine layers upon the early crust. Volcanic
craters opened under water, and poured out liquid mineral matter, that
flowed over the sea bottom before it cooled. Imagine the commotion that
agitated the water as these submerged chimneys blew off their lids, and
discharged their fiery contents! It was long before the sea was cool
enough to be the home of living things.

The layers of rock that formed under the sea during this period of the
earth's history are of enormous thickness. They were four or five miles
deep along the Laurentian Hills. They broadened the original granite
ridge by filling the sea bottom along the shores. The backbones of the
Appalachian system and the Cordilleras were built up in the same
way--the oldest rocks were worn away, and their debris built up newer
ones in strata.

When these layers of rock became dry land, the earth's crust was much
more stable and cool than it had ever been before. The vast
rock-building of that era equals all that has been done since. The
layers of rocks formed since then do not equal the total thickness of
these first strata. So we believe that the time required to build those
Archaean rock foundations equals or surpasses the vast period that has
elapsed since the Archaean strata were formed.

The northern part of North America has grown around those old granite
ridges by the gradual rising of the shores. The geologist may walk along
the Laurentian Hills, that parted the waters into a northern and a
southern ocean. He crosses the rocky beds deposited upon the granite;
then the successive beds formed as the land rose and the ocean receded.
Age after age is recorded in the rocks. Gradually the sea is crowded
back, and the land masses, east, west, and north, meet to form the
continent. Nowhere on the earth are the steps of continental growth
shown in unbroken sequence as they are in North America.

How long ago did those first islands appear above the sea? Nobody
ventures a definite answer to this question. No one has the means of
knowing. But those who know most about it estimate that at the least one
hundred million years have passed since then--one hundred thousand
thousand years!

A STUDY OF GRANITE

In Every village cemetery it is easy to find shafts of gray or speckled
granite, the p