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subsequent erosion. Lyell concludes that the literal record of catastrophic
faunal turnover really represents a continuous change of life filtered through
ordinary laws of sporadic sedimentation: "If this train of reasoning be
admitted, the frequent distinctness of the fossil remains, in formations
immediately in contact, would be a necessary consequence of the existing
laws of sedimentary deposition, accompanied by the gradual birth and death
of species" (III, 32-33).
Lyell then switches metaphors to illustrate the important corollary that signs
of disturbance in an illusory transition need bear no relation to the actual
causes of change. Suppose that a modern eruption of Mt. Vesuvius buried an
Italian city atop Herculaneum. The abrupt change in language and
architecture, as seen in the archaeological record, would not only be illusory,
but also quite unrelated to the catastrophe of volcanic eruption.
As Lyell defended gradualism by probing behind the literal appearance of
catastrophe, he supported the second substantive uniformity (of state) with a
similar admission and resolution. He also granted that several vectors of
directional change ran through the geological record read literally—older
rocks tend to be denser, harder, and more altered by heat and pressure;
climates (at least in the northern hemisphere) have become harsher, as
indicated by sediments and the fossils they contain; life itself (at least for
vertebrates) has become more complex. Lyell argued that each apparent
vector is an illusion produced by directional biases of preservation acting
upon a uniform world in steady state.
Lyell again relied upon metaphor to express these (then) unfamiliar and
crucial arguments. Suppose that a collector of insects shipped specimens
from a tropical land to England, with a minimum transport of two months,
and suppose that these organisms lived little longer than two months (and did
not breed in captivity). Englishmen would then see only aged adults.
Likewise, old rocks are often contorted and metamorphosed, younger rocks
evenly layered and less dense. Many geologists had viewed this directional
change in strata as a sign of decreasing intensity in geological forces,
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