Lyell's first visit to Sicily was in 1828 when he journeyed to Mount Etna to gather evidence for his theory that geological change was gradual and took place over millions of years. This ran counter to the Upheaval theory which was current at the time. This theory held that geological change was the result of a number of catastrophic events. He revisited Sicily in 1857 and 1858 to gather further evidence against the Upheaval Theory. He proved beyond doubt that the geology of Mount Etna was built up by a series of small eruptions rather than by one or two huge events. He was greatly aided in his research in Sicily by members of the Gemmellaro family, Carlo, Guiseppe and Gaetano Giorgio who were local geologists. See also separate correspondence files in the A-Z series.