Strongly influenced by Lyell's Principles of Geology, Darwin during the Beagle voyage developed a highly theoretical geology based on premises of continental uplift and oceanic subsidence. From the beginning he used his theoretical interpretations to validate and select his field observations. These he interpreted and communicated largely in the form of profile diagrams, of South American shorelines, Andean tectonic structures, and coral reef development. His published works from the voyage are very sparsely illustrated, except for profile diagrams, and contain remarkably few maps. Of the latter all are derivative except one. The one exception is his 1842 map of the distribution of coral reefs, which he uses as a theoretical argument to delineate areas of elevation and subsidence in the oceans, implicitly illustrating the formal logical analogy between the nature of theory and the nature of maps. The illustrations in general illustrate the contrast between Darwin's verbal facility in describing landscapes and evoking mood, and his general inability to translate his images into visual representations.