The essay examines the function and the meaning of documentary images by examining the geological image collection of the Swiss natural philosopher Conrad Gessner. Gessner?s interest in pictorial documentation can only be understood in the context of his special interest in the formal aspects of nature. His approach marked a turning point in the history of natural philosophy and would be unthinkable without the pictorial techniques used to collect and document the objects of his research. By reconsidering philosophical definitions of (...) form and matter, he set geoscience on a new philosophical foundation. This reorientation is closely connected to the metaphysics of nature. Both aspects were essential to the establishment of a new scientific approach, in which the old epistemological technique of studying texts was coupled to a new source of knowledge: the study of images. (shrink)