Lyell visited Paris that year and met several famous scientists including Georges Cuvier, Alexander von Humboldt, and Constant Prévost. The alternating layers of marine and freshwater formations in the Paris basin intrigued Lyell, and he realized that minor changes in a geological barrier could explain the pattern. In 1824 Lyell accompanied Buckland on a trip through scotland during which he pondered the Parallel Roads of Glen Roy, admired the granite veins of Glen Tilt, and studied limestone and marl deposits in small freshwater lakes in Bailie. He read his first paper to the Geological Society in December of that year, "On a Recent Formation of Freshwater Limestone in Forfarshire," followed by more on Tertiary exposures of the Hampshire coast of England. In 1826 an article he published in the Quarterly Review, "Transactions of the Geological Society of London," summarized the current knowledge and major areas of investigation in geology. While composing this review, he began to believe that ordinary geological forces such as earthquakes and volcanoes could explain unusual phenomena such as the presence of sedimentary strata formed on the ocean floor but found on mountain summits. The Royal Society of London elected Lyell a fellow in 1826.

Lyell continued to make geological excursions, including trips to France, Italy, and Scotland, collecting data wherever he visited. One journey in 1828 that affected his views about geological processes brought him to France, Germany, and Italy with Scottish geologist Roderick Murchison. In central France Lyell found analogies between the geological past and formations currently developing. Again, he thought modern processes must resemble those that had shaped ancient formations. The revelation struck him that the appearance of strata was determined by the conditions when it was laid, not just by age. Similar conditions in the present day could replicate a layer with characteristics in common with an ancient stratum; thus modern conditions and geological processes must resemble those of the past.

In Italy he observed layers of lava exposed in the mountain walls of Etna, fossils of living species buried at its base, and younger uplifted strata with large percentages of extant species. These observations led to his conclusion that the volcanic mountain had been formed relatively recently, layer by layer. Accruing evidence caused him to doubt the neptunist doctrine, and he observed more physical support for the vulcanists, who believed that volcanic activ ity was responsible for the major changes in the construction of the Earth's surface. Cuvier believed that life on the Earth was periodically destroyed through the violent actions of catastrophic events such as floods. Lyell rejected this idea of catastroph-ism. Instead he believed that geological changes were caused gradually by ordinary geological processes, a theory called uniformitarianism, proposed by Scottish geologist James Hutton in 1785. Lyell believed that the steady accumulation of changes from earthquakes and volcanic activity caused the elevation and disturbances found in the sedimentary rocks. He imagined that geological processes he directly observed also occurred in the past, forming analogous structures.

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