FAMOUS GEOLOGISTS/Walther 243 Early in his career, Walther set himself the aim of ‘modernizing’ Lyell’s uniformitarianism Thus he undertook journeys to study as many geological conditions and environments as possible, but he focused on two fields in particular: shallow marine environments (including reefs) and deserts At the time when he wrote his principal works, palaeontology, stratigraphy, and tectonics dominated geology in the universities, but Walther did not focus on these fields Sedimentary rocks were chiefly studied because of their fossil content, useful for stratigraphy, and not because they illustrated former environments Strongly influenced by Haeckel, the German apostle of Darwinism, Walther applied his ideas to geology by looking at the mode of formation of sediments, and the processes that formed rocks, not just their characteristics His credo was: ‘‘Aus dem Sein erklaăren wir das Werden (From the present state [of a rock] we explain its origin) But he was well aware that some past processes not occur today Though physical laws remain the same, geological conditions vary and may even be unique With this dynamic approach, Walther was able to integrate climatological, sedimentological, palaeontological, and other aspects into Amanz Gressly’s ‘facies’ concept (1838), which was the basis for Walther’s comprehensive consideration of facies His view of the succession of palaeoenvironments was expressed in the ‘Law of Facies’, which was subsequently named after him (even though it had already been found by Gressly): ‘‘Es ist ein Grundsatz von weittragender Bedeutung, dass primaer sich nur solche Facies und Faciesbezirke geologisch uă berlagern koă nnen, die in der Gegenwart nebeneinander zu beobachten sind’’ (‘‘It is a principle of far-reaching importance that only the facies or facies areas that are at present adjacent to one another can be geologically superimposed upon one another’’) (Walther [1894], p 979; see also Middleton [1972]) In other words, the relative horizontal distribution of sediments with their organic content will be transformed into a vertical distribution, having a chronological order Gressly found the rule during his extended fieldwork for his admirable monograph on the Swiss Jurassic near the town of Solothurn, where he carefully studied the facies changes Fifty years later, Walther discovered Gressly’s study of 1838 anew, when he was working for his volume on lithogenesis He explained and discussed this idea in detail in the first of three chapters on facies in his most interesting third volume (Lithogenesis of the Present) of his fundamental work, Einleitung in die Geologie als historische Wissenschaft (1894) This discussion of the ‘law’ was only a minor part of the total corpus of his work, but it is on this that his present reputation chiefly rests Walther stressed the importance of organisms in geological processes and vice versa: biogeology The dependence of biocenoses (groups of organisms living together, forming natural ecological units) on their substrates means that lithology should have priority over palaeontology He mentioned, for example, that the empty shells of index fossils can be transported over long distances and may, therefore, give false stratigraphic results With his zoological background of comparative anatomy Walther thus advocated ‘comparative lithology’ This concept improved stratigraphy substantially and Amadeus W Grabau (1870–1946) paid tribute to it by dedicating his classic Principles of Stratigraphy (1913) to Walther The first of the other two volumes of Walther’s Introduction to Geology as Historical Science (see above), Bionomie des Meeres, was a treatise on marine biogeology that dealt with the interactions between the sea floor, fauna, and flora; beyond that it also had chapters on oceanography (He had previously published a popular booklet on general oceanography in 1893.) The second volume was mostly a collection of faunal lists All Walther’s pioneering work was undertaken in his years in Jena One of his later publications was the voluminous Allgemeine Palaă ontologie (General Palaeontology) (1927) He wanted to give a summary of all the topics he had thought and taught about, and this was a lot The book contained a wealth of varied ideas, though regrettably a number of them were already outdated by the time the book appeared With its 809 pages, it presents difficult, yet still inspiring reading For Walther, theories were much more important than details Special Contributions Shallow Marine Walther’s final study on the sediments of Dove Bank (Taubenbank, 1910), a shoal in the Gulf of Naples, was a classic He compared his first maps of 1884 with the latest findings of 1910 to evaluate the changes caused by volcanic activity (Vesuvius produced a great ash-fall in 1906) and the unusual storms of the intervening years (an early look at event stratigraphy!) His former studies of the rock-forming calcareous algae (1885) enabled him to compare his old and new results He showed that coralline algae spread rapidly, consolidating sediments within 25 years Perhaps even more interesting was Walther’s application of biological experiments to explain bioturbation, which he stated could occur down to 15 cm He also measured the digging velocity of mussels Using