surface of the earth, accompanied by the
introduction of a new set of animals, though the changes in the organic
world are not so striking as those which coincide with the
mountain-upheavals. Still, to the eye of the geologist they are quite as
distinct, though less evident to the ordinary observer. To these divisions
it seems to me that the name of Period is rightly applied, because they
seem to have been brought about by the steady action of time, and by
gradual changes, rather than by any sudden or violent convulsion.

It was my good fortune to be in some degree connected with the
investigations respecting the limitation of Periods, for which the geology
of Switzerland afforded peculiar facilities. My early home was near the
foot of the Jura, where I constantly faced its rounded domes, and the
slope by which they gently descend to the plain of Switzerland. I have
heard it said that there is something monotonous in the continuous
undulations of this range, so different from the opposite one of the Alps.
But I think it is only by contrast that it seems wanting in vigor and
picturesqueness; and those who live in its neighborhood become very much
attached to the more peaceful character of its scenery. Perhaps my readers
will pardon the digression, if I interrupt our geological discussion for a
moment, to offer them a word of advice, though it be uncalled for. I have
often been asked by friends who were intending to go to Europe what is the
most favorable time in the day and the best road to enter Switzerland in
order to have at once the finest impression of the mountains. My answer is
always,--Enter it in the afternoon over the Jura. If you are fortunate,
and have one of the bright, soft afternoons that sometimes show the Alps
in their full beauty, as you descend the slope of the Jura, from which you
command the whole panorama of the opposite range, you may see, as the day
dies, the last shadow pass with strange rapidity from peak to peak of the
Alpine summits. The passage is so rapid, so sudden, as the shadow vanishes
from one height and appears on the next, that it seems like the step of
some living spirit of the mountains. Then, as the sun sinks, it sheds a
brilliant glow across them, and upon that follows--strangest effect of
all--a sudden pallor, an ashy paleness on the mountains, that has a
ghastly, chilly look. But this is not their last aspect: after the sun has
vanished out of sight, in place of the glory of his d