6 ideas
The former changes of the Earth's surface should be explained by causes observably operating today (rain, rivers, tides, volcanoes, earthquakes, sedimentation), not by unobserved forces invoked for the occasion. Because these agents can be measured now, they give geology a testable basis. Speculation about past events is then limited by what known processes can actually do.
The size of a result is not evidence of a violent cause. It can equally be the product of a small rate multiplied by a long duration.
When observers assume the Earth is young, they must explain large features with sudden, violent, extraordinary events, because there is no time for ordinary processes to work. The belief in catastrophes follows from a compressed timescale, not from the rocks themselves. Grant sufficient time and the need for catastrophes disappears.
The Roman columns of the Temple of Serapis near Naples bear a band of holes bored by marine mollusks well above the ground. This shows the land sank below sea level and later rose again within historical times, without toppling the columns.
Tertiary rock layers can be ordered by the percentage of their fossil shell species that still survive today. More living species means younger rock. On this basis Lyell named the Eocene, Miocene, and Pliocene. The method turns the gradual turnover of species into a clock for reading the relative age of formations.
The rock and fossil record is fragmentary, because deposition happens only in certain places and much is later eroded. Abrupt breaks between strata therefore reflect missing pages rather than sudden global revolutions. Apparent discontinuities should first be read as gaps in preservation before they are read as evidence of catastrophe.