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In the late 1600s, naturalists began to argue that fossils are of organic nature and origin, rather than having grown in the rock. This is a plate from Scillo's treatise Vain Speculation Undeceived by Sense (1670). These shell fossils were strong evidence, as they differed little from known living animals.
More difficult were the cases of fossils that looked like nothing known on earth. This giant ammonite (about 2 feet in diameter) was used by Martin Lister in The History of Shells (1692) to argue against organic origins. He was a great expert on seashells, and thus his conclusions about lack of similarity carried great weight. Agreeing with Lister was Robert Plot, the Professor of Chymistry at Oxford, who acknowledged in his Natural History of Oxfordshire (1677, pp. 111-12) "the great Question now so much controverted in the World: Whether the Stones we find in the Forms of Shell-fish be Lapides fui generis, naturally produced by some extraordinary plastic virtue, latent in the Earth or Quarries where they are found? Or, whether they rather owe their Form and Figuration" to the "mud, clay, and petrifying juices" that turned them into stones. Admitting it appeared as an open question in debate, his "mature deliberation" left him "inclined rather to the opinion" that the fossils could not be the remains of animals. The difficulties seemed too improbable that they could have been formed, and placed in uplands, by the Deluge in the days of Noah" or a local flood.
Niels Stensen [Steno] argued the more difficult case for organic origins of all fossils, in widely noted work from 1667-70. By analyzing the structure of the fossil rocks, he was able to show a similarity to living animals and difference from crystal growth in other rocks. But the issue was not resolved in the late 1600s, with prominent naturalists such as John Ray and Robert Hooke staking out divergent views. Rudwick, in his The Meaning of Fossils (1985), concludes that the issue remained controversial for half a century. Steno's view, that the evidence of rock strata as sequential layers provides a new vision of an expanded history of life, became standard in the early 1700s, but only after being promoted by John Woodward in Essay toward a Natural History of the Earth (1695).
By the mid-1700s, naturalists had moved to accepting fossils as remains of ancient organisms. The result was a new interest in collecting, in careful documentation and mapping, and in drawing conclusions about the history of the earth. One of those conclusions inevitably became an expanded age of the earth; another was radical new ideas about the forms of life on an ancient world.
By the end of the 1700s, geologists accepted a greater age of the earth, and understood that many species of fossils could not be found today. Mapping of fossil distributions had also left puzzles, such as seashells on mountaintops and alternating layers of terrestrial and marine fossils. Attempts to fit such evidence to the Biblical Deluge were becoming too obviously strained and speculative for the tastes of Newtonian naturalists, who searched instead for existing physical processes that could have caused the regularity of observed phenomena. Although himself too grand a visionary and speculator for many, Buffon's conclusions about a sequence of past epochs, and their evidence in the observable structure of the earth, inspired naturalists.
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