THE EVOLUTION OF ILLUSTRATION PRACTICES IN GEOLOGY TEXTS DURING THE GOLDEN AGE OF GEOLOGY (1788-1840)

An historical investigation into the types of illustrations in the Golden Age of Geology (1788-1840) revealed the nature and progression of graphic representation at the dawning of geology as a science. Using Edward Tufte's three-volume theory of graphic design, a categorization scheme of illustrations emerged to include proxies, labeled proxies, inferred representations, mathematical relationships, and small multiples. The illustrations were analyzed as to their data density, chartjunk, multivariate properties, and graphic modification. After an exhaustive investigation of texts, the categories and their boundaries were delineated based upon comparative studies of the graphics' typical features. Four broad categories of graphic trends were revealed: 1) early pictorial or proxy representations, 2) emergence of labeled graphics with the first geology texts, 3) a period of grand or elaborate illustration, and 4) a period where numerous graphics were inserted within texts.

The graphic density of published texts changed noticeably within the Golden Age of Geology. In the earliest publications, illustrations were used sparingly, if they were present at all. The popular use of wood engravings in the later texts allowed easier and economical reproduction of graphic images; texts published late in the age of focus tended to have more illustrations than texts published at the beginning. Hypothesis testing around a correlation coefficient showed significance at the 99% confidence level for a relationship between the publication year and the graphic density of texts.

Further research into the history of publishing revealed that the illustrative trends paralleled but lagged innovations in the printing industry. Changes in illustration type also reflected societal changes of an emerging educated class as well as changes within the targeted audiences for geology texts.

Although the inclusion and types of graphics evolved substantially in the formative years of geology as a separate science, illustrative design had not yet reached its present level as far as complexity, layering of data, and causality. Even at the end of the Golden Age of Geology, most illustrations were non-mathematical, and indicate that geology was still in a pre-graphing phase.