" It has
yielded specimens of about a thousand species of Tertiary
insects. Near the large ancient lake, of which it marks the site,
was a volcano, and the fine ash yielded from the cone seems to
have buried myriads of insects in the water. At Oeningen a
similar lake-deposit has, although only a few feet thick, yielded
900 species of insects.
Yet these rich and numerous finds throw little light on the
evolution of the insect, except in the general sense that they
show species and even genera quite different from those of
to-day. No new families of insects have appeared since the
Eocene, and the ancient types had by that time disappeared. Since
the Eocene, however, the species have been almost entirely
changed, so that the insect record, from its commencement in the
Primary Era, has the stamp of evolution on every page of it.
Unfortunately, insects, especially the higher and later insects,
are such frail structures that they are only preserved in very
rare conditions. The most important event of the insect-world in
the Tertiary is the arrival of the butterflies, which then appear
for the first time. We may assume that they spread with great
rapidity and abundance in the rich floral world of the
mid-Jurassic.
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