The picture on the title page is of the classical ruins of the Temple of Serapis in Rome. The person on the rock is contemplating the passage of time and the destruction of an older world, which also left the evidence of its existence behind. Lyell is using the popular fascination with classical archaeology to point the reader to the marks and evidences of past events, accessible to the modern observer. The columns show watermarks of various levels of submersion over time. Even more tellingly, the columns have boreholes (located 12 to 20 feet up) made by marine mollusks that must have been underwater. Clearly, even within the timescale of human history, the land had subsided and risen again, or else the sea had risen and subsided. These were the cycles of geological history, and most importantly, they could not have been "catastrophic" -- sudden or violent -- because the pillars of the ruin were still standing. Geological change meant gradual processes.

Skillful in rhetoric, Lyell described the view of the ancient earth being dramatically different from the present as a prejudice and superstition, to be replaced by good Newtonian science and progressive advance in knowledge. His first principle we could also call actualism: the causes of the past are the same as the causes in the present. Processes making phenomena are uniform, acting as causes in the same way today as in the past. Actualism requires another uniformity -- the uniformity (constancy) of natural laws not only every place but throughout time. That makes it possible to make scientific inferences about the past, beyond direct observation. This was the principle that Hutton promoted to good effect -- that the only way to have a geological science was to be able to make rules of nature out of observations. Thus it sounds rather like Newton's rules for simplicity, universality, and proper deduction.

Lyell applied these principles to the data of geology, arguing as well for the uniformity of rates. The world changes in slow and gradual steps, building up small causes over long times to great effect. This was his argument against invoking catastrophes. The catastrophic causes we can see, such as earthquakes and volcanic eruptions and erosions, are recast as small and local, and at the same frequency and intensity as in the past. This eventually became accepted among geologists as a guiding principle, although it was resisted by leading geologists in the 1830s.

Lyell also argued for the uniformity of a steady-state, in order to deny progressive development in the earth's history. This was a part of his strong argument against Lamarck's theory of evolutionary changes of species. For Lyell, the geological earth is in a dynamic balance with no real direction of progress. Rejecting progressive development was also controversial and resisted. For most geologists (including Cuvier, Agassiz, Buckland, and Sedgwick), progressive development did not have to imply evolution, if the changes in fossil species were seen as special creations.

In the principles of uniformity, Lyell also provided a way to see the discontinuous stratigraphy data in a new way. They could be the result of dynamic processes that are uniform (continuous, gradual) --

"It has been truly observed, that when we arrange the fossiliferous formations in chronological order, they constitute a broken and defective series of monuments: we pass without any intermediate gradations from systems of strata which are horizontal, to other systems which are highly inclined -- from rocks of peculiar mineral composition to others which have a character wholly distinct -- from one assemblage of organic remains to another, in which frequently nearly all the species, and a large part of the genera, are different. These violations of continuity are so common as to constitute in most regions the rule rather than the exception, and they have been considered by many geologists as conclusive in favour of sudden revolutions in the inanimate and animate world. We have already seen that according to the speculations of some writers, there have been in the past history of the planet alternate periods of tranquillity and convulsion, the former enduring for ages, and resembling the state of things now experienced by man; the other brief, transient, and paroxysmal, giving rise to new mountains, seas, and valleys, annihilating one set of organic beings, and ushering in the creation of another."

His object was to show that

"these theoretical views are not borne out by a fair interpretation of geological monuments. It is true that in the solid framework of the globe we have a chronological chain of natural records, many links of which are wanting: but a careful consideration of all the phenomena leads to the opinion that the series was originally defective -- that it has been rendered still more so by time -- that a great part of what remains is inaccessible to man, and even of that fraction which is accessible nine-tenths or more are to this day unexplored."

Not only can we not observe much of the history of past life, with such a sparse fossil record. The creation of new species itself was for Lyell not observable in the present -- and thus not a cause that he could deduce. His critics within geology thought his "actualist" reasoning was too limited, as Whewell maintained. They also concluded from fossil evidence (such as tropical plants in Europe) that the past Earth had been much warmer than at present. They used the cooling theories of Buffon, Laplace, and Fourier to help explain the different epochs of geological history, but Lyell rejected this use of physics to aid the inference of past causes.

And what about the fossils of extinct life? Contrary to Lamarck, Lyell saw the fossil record as showing no trends or directions from simple to complex organisms. Lyell had to conclude, to be consistent with his principles, that the lack of progress in the fossil record meant that eventually, once more fossils had been discovered, even modern or complex life- forms would be found somewhere in older layers. If new species did appear in the history of life, the cause was a natural law, even if it also was an "exertion of creative power."

The new theory of course did not persuade everyone. One striking case against the sufficiency of Lyell's "actualist" and "uniform" processes was the shape of many European valleys.  Glacial scouring action as a cause of the shape of landscapes had not yet been proposed, and erosion did not seem able to produce the particulars of all formations. In this cartoon, dedicated to Professor Buckland, the artist Henry de la Beche mocks the power of erosion alone to  produce the river valley (the little boy peeing is Frank, the professor's son: "Bless the baby! What a Walley he have a-made!!!").    

Controversial on several of the central issues in geology of the early 1800s, Lyell's work did provide an extraordinarily useful catalogue of the operating causes in geological phenomena, a guide to reasoning, and great inspiration for a generation of geologists (including Charles Darwin in particular).