... found in the most ancient chapters of the geological record, so many of their leaves have been destroyed and so far have their pages been defaced. Omitting structures whose organic nature has been questioned, there are left to mention a tiny seashell of one of the most lowly types,—a DISCINA from the pre- Cambrian rocks of the Colorado Canyon,—and from the pre-Cambrian rocks of Montana trails of annelid worms and casts of their burrows in ancient beaches, and fragments of the tests of crustaceans. These diverse forms indicate ... — The Elements of Geology • William Harmon Norton
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