een hundred feet above the sea, and is
thirty-four feet in diameter at the ground. This is as large as the
very largest specimens of the _Sequoia gigantea_, but it may have
spread out more at the base and have been somewhat smaller above,
though this is not a special characteristic of the species.

[Illustration]

WHAT IS EVOLUTION?

(FROM THE ATLANTIC MONTHLY, MARCH, '93.)

BY PROFESSOR E.S. HOLDEN.

[Illustration]

I was once trying to tell a boy, a friend of mine, what the scientific
men mean by the long word _Evolution_, and to give him some idea of
the plan of the world. I wanted an illustration of something that had
grown--evolved, developed--from small beginnings up through more and
more complicated forms, till it had reached some very complete form. I
could think of no better example than the railway by which we were
sitting. The trains were running over the very track where a
wagon-road had lately been, and before that a country cart-track, and
before that a bridle-path, and before that again a mere trail for
cattle. So I took the road for an example, and tried to show my boy
how it had grown from little things by slow degrees according to laws;
and if you like, I will try to tell it again.

Just as one can go further and further back, and always find a bird to
be the parent of the egg, and an egg to be the parent of that bird, so
in the history of this road of ours; we may go back and back into the
past, always finding something earlier, which is the cause of the
something later. The earth, the planets, and the sun were all a fiery
mist long ago. And in that mist, and in what came before it, we may
look for the origin of things as they are. But we must begin
somewhere. Let us begin with the landscape as we see it now,--hills,
valleys, streams, mountains, grass,--but with only a single tree.

We will not try to say how the tree came there. At least, we will not
try just yet. When we are through with the story you can say just as
well as I can.

Suppose, then, a single oak-tree stood just on that hillside thousands
and thousands of years ago. Grass was growing everywhere, and flowers,
too. The seeds came with the winds. Year after year the oak-tree bore
its acorns, hundreds and hundreds of them, and they fell on the grass
beneath and rolled down the smooth slopes, and sprouted as best they
could,--most of them uselessly so far as producing trees were
concerned,--but each one did its duty and