For instance, until recently not a land-shell was known belonging to either of these vast periods, with the exception of one species discovered by Sir C.

Lyell and Dr.

Dawson in the carboniferous strata of North America; but now land-shells have been found in the lias.

In regard to mammiferous remains, a glance at the historical table published in Lyell's Manual, will bring home the truth, how accidental and rare is their preservation, far better than pages of detail.