Introduction: writing about twentieth century geology
In a classic paper by the late Yale historian of science, Derek De Solla Price (1965), based mainly on the study of citations in a single scientific research field, it was shown how citations in a developing research area have a strong 'immediacy effect'.1 Citation was found to be at a maximum for papers about two-and-a-half years old, and the 'major work of a paper … [is] finished after 10 years', as judged by citations. There were, however, some 'classic' papers that continue to be cited over long periods of time, and review papers specifically discussing the earlier literature. There appears to be a need for such review papers after the publication of about thirty to forty research papers in a field. And the knowledge is synthesized in book form from time to time.