At The Mountains of Madness - H. P. Lovecraft

"I am forced into speech because men of science have refused to follow my advice without knowing why. It is altogether against my will that I tell my reasons for opposing this contemplated invasion of the antarctic—with its vast fossil hunt and its wholesale boring and melting of the ancient ice caps. And I am the more reluctant because my warning may be in vain."

On an expedition to Antarctica, Professor William Dyer and his colleagues discover the remains of ancient half-vegetable, half-animal lifeforms. The extremely early date in the geological strata is surprising because of the highly-evolved features found in these previously unknown life-forms.