which we trace, by
volcanoes and earthquakes, on either side of the Pacific. Others, again,
connect the shape of our great masses of land, which generally run to
a southern point, with this early catastrophe. But these interesting
speculations have a very slender basis, and we will return to the story
of the development of the earth.

The last phase in preparation for the appearance of life would be the
formation of the ocean. On the lines of the generally received nebular
hypothesis this can easily be imagined, in broad outline. The gases
would form the outer shell of the forming planet, since the heavier
particles would travel inward. In this mixed mass of gas the oxygen and
hydrogen would combine, at a fitting temperature, and form water.
For ages the molten crust would hold this water suspended aloft as a
surrounding shell of cloud, but when the surface cooled to about 380
degrees C. (Sollas), the liquid would begin to pour on it. A period of
conflict would ensue, the still heated crust and the frequent volcanic
outpours sending the water back in hissing steam to the clouds. At
length, and now more rapidly, the temperature of the crust would sink
still lower, and a heated ocean would settle upon it, filling the
hollows of its irregular surface, and washing the bases of its
outstanding ridges. From that time begins the age-long battle of the
land and the water which, we shall see, has had a profound influence on
the development of life.

In deference to the opinion of a number of geologists we must glance
once more at the alternative view of the planetesimal school. In their
opinion the molecules of water were partly attracted to the surface out
of the disrupted matter, and partly collected within the porous outer
layers of the globe. As the latter quantity grew, it would ooze upwards,
fill the smaller depressions in the crust, and at length, with the
addition of the attracted water, spread over the irregular surface.
There is an even more important difference of opinion in regard to the
formation of the atmosphere, but we may defer this until the question
of climate interests us. We have now made our globe, and will pass on
to that early chapter of its story in which living things make their
appearance.

To some it will seem that we ought not to pass from the question of
origin without a word on the subject of the age of the earth. All that
one can do, however, is to give a number of very divergent estimates.
Ph