published in 1795). The central argument in Principles was that "the present is the key to the past": that geological remains from the distant past could, and should, be explained by reference to geological processes now in operation and thus directly observable.

The book is notable for being one of the first to use the term "evolution" in the context of biological speciation.

In Lyell's work, he described the three rules he believes to cause the steady change of the Earth. The first rule is

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