Lyell was a lawyer by profession and his Principles of Geology (published in 3 volumes, 1830-33) is a powerful mixture of argument and rhetoric. Darwin read Lyell before and during the voyage of the Beagle and became a convinced Lyellian. Many of Darwin's early papers—e.g., on the formation of coral atolls, on the parallel roads of Glen Roy—were deliberate attempts to explain geological features in a uniformitarian way.
Lyell self-consciously aimed to present his brand of uniformitarianism as the scientific way of doing geology. But many of his opponents, including the so-called "catastrophists," were also reputable scientists: e.g., Cuvier, Whewell, Agassiz, Buckland, Sedgwick, Murchison. It is wrong to think that Lyell's critics were religious fundamentalists who believed that the earth was created in the very recent geological past, or that they relied on a Noachian deluge in their theories.
Some General Remarks
Lyell's approach to geology had its origin in James Hutton's Theory of the Earth (1795) and the dispute between the "Vulcanists" (Hutton, Playfair) and the "Neptunists" (Werner). Hutton found in the earth's geology "no vestige of a beginning, —no prospect of an end." Lyell was also strongly committed to a steady-state, non-directional, non-progressive view of the earth. There was continual, gradual change but no overall direction or trend. Thus, Lyell rejected out of hand the contention that the earth had been very hot (molten) when it was first formed and had been cooling ever since. It was as if Lyell denied the relevance of physics, astronomy, and cosmology to geology.
Lyell's non-directionalism put him in an awkward position when it came to the history of living things. Lyell acknowledged that many species had become extinct. But, he insisted:
Lyell's "Presentism" or "Actualism"
The subtitle of Lyell's Principles was "Being an Attempt to Explain the Former Changes of the Earth's Surface, by Reference to Causes Now in Operation." It is pretty clear that in restricting geological theories to causes that we can observe acting in the present, Lyell wanted to rule out catastrophes on methodological grounds. No catastrophes are observed in the present. So, it is illegitimate to postulate them acting in the past in order to explain the present state of things. Lyell was appealing to a particularly strong version of the vera causa principle. He was in close contact with Herschel during this period and was well-acquainted with Herschel's views prior to the publication of the Preliminary Discourse in 1830.
Many geologists (Sedgwick, Conybeare, Agassiz) rejected Lyell's presentism. Probably the best criticisms of it were offered by Whewell.
Lyell's Kind and Degree Uniformitarianism
Lyell, no less than the catastrophists, believed in the uniformity of the laws of nature. Catastrophes, even Buckland's gigantic flood, were presumed to have natural causes. They were not proposed as divine miracles. (Much of what had prompted Buckland’s theory was eventually explained by the Ice Age.) The one exception, that even Lyell made, was the origin of species which Lyell described as being caused by the "exertion of creative power."
So, the issue was not the uniformity of the laws of nature but the kinds of causes that were legitimate in geological theories. According to Lyell, the geologist should accept that "no causes whatever have from the earliest time to which we can look back, to the present, ever acted but those now acting, and that they never acted with different degrees of energy from that which they now exert." (Letter from Lyell to Roderick Murchison, 1829).
Historians summarize Lyell's position by distinguishing between his "kind uniformitarianism" and his "degree uniformitarianism." Not only was geology to restrict its hypotheses to the same kind of causes as those acting now, but also it must further restrict the intensity of those causes to the range of intensity that we find now.
Degree and kind uniformitarianism together rule out the possibility of a developmental theory of the earth. If the kind and intensity of causes have always remained the same, then the earth cannot have changed to a significant extent throughout its long history.
While many geologists might agree that it is legitimate and desirable to explain the past using present causes, while must it be illegitimate to introduce additional causes, of a kind no longer active, when this becomes necessary?
Also, many current causes are notoriously variable in their intensity. Why then cannot we postulate, say, volcanoes of much greater power in the past, especially if we believe (as many catastrophists did) that the earth was much hotter in the past.
Lyell was notoriously accommodating when it came to deciding what constituted the present. In this way he was able to avoid any precise specification of what would constitute a difference in kind and a difference in degree of geological causes. For example, it is not clear when a very large flood becomes a new kind of cause as opposed to being classified as high degree of flooding.
W. F. Cannon, "The Uniformitarian-Catastrophist Debate," Isis 51 (1960) 38-55.
W. F. Cannon, "The Impact of Uniformitarianism: Two Letters from John Herschel to Charles Lyell, 1836-37," Proceedings of the American Philosophical Society 105 (1961) 310-14.
L. Wilson, Charles Lyell, The Years to 1841: The Revolution in Geology (1972).
G. C. Gillispie, Genesis and Geology (1959).
M. J. S. Rudwick, "The Strategy of Lyell's Principles of Geology," Isis 61 (1970) 4-33.
M. J. S. Rudwick, "A Critique of Uniformitarian Geology: A Letter from D. Conybeare to Lyell, 1841," Proceedings of the American Philosophical Society 101 (1967) 272-87.
M. Ruse, "Charles Lyell and the Philosophers of Science," British Journal for the History of Science 9 (1976) 121-31.
R. Laudan, "The Role of Methodology in Lyell's Science," Studies in the History and Philosophy of Science 13 (1982) 215-49.
S. J. Gould, "Is Uniformitarianism Necessary?" American Journal of Science 263 (1965) 223-8.
S. J. Gould, "Uniformity and Catastrophe," in Ever Since Darwin (1977) 147-52.