244 FAMOUS GEOLOGISTS/Walther a ‘hyperactualist’ method, he explained the formation of calcareous sands by keeping crayfish and mussels together in an aquarium and finding that four crayfish of 12–18 cm length worked a load of 580 g of mussels into detritus within 12 days The final weight was 240 g A ‘fossil example’ was provided by his study of the fauna of the Solnhofen sediments (Upper Jurassic, Bavaria, South Germany) (1904), a contribution for a volume in honour of Haeckel’s 70th birthday Walther tried to show all features of a biotope by determining the frequency of marine and land fossils at various localities in the Solnhofen sediments He noted the lack of freshwater and brackish species, and localized the presence of plant debris; by the decreasing frequency of occurrence of the planktonic crinoid Saccocoma, from a centre outwards in all directions, he concluded that the greatest depth of water had been in this central area Besides his own observations, Walther used data from all available collections and fossil lists for his demonstration of the Solnhofen biotope Unfortunately, this exemplary study was almost hidden among the zoological articles in the Haeckel volume and in consequence was overlooked by many geologists Reefs During his early studies (1885) in the Gulf of Naples, Walther became interested in the growth of calcareous algae He compared his marine findings with what could be found in Tertiary sediments in Sicily and with Triassic alpine rocks, and concluded that lithification takes place concomitantly with deposition, leading to the formation of structureless limestones A further step towards greater understanding of reefs was achieved as a result of his voyages to the south coast of Sinai (1886) and to the Palk Strait (India) (1888–1889) Walther also emphasized that reefs are traps for considerable amounts of sediments, which form up to 60% of the whole reef complex Further, he noted the importance of tectonic movements, sea level changes, and topography for the reef growth (elevations are preferred places), laterally or vertically Deserts The journey of 1886 along the Sinai coast, with a return along the Egyptian side of the Red Sea through the Galala Desert offered Walther splendid opportunities for the study of desert environments, which he was subsequently able to extend in the USA (1891), central Asia (1897), Egypt (1911), and Australia (1914) He soon recognized the importance of aeolian erosion, which previously had not been much taken into account Consequently, his first publication on deserts had the provocative title Die Denudation in der Wuă ste und ihre geologische Bedeutung (1892) (Desert Denudation and its Geological Importance) and provoked many controversies In fact, he tended to exaggerate the notion of desert erosion and neglected the influence of periods with strong fluviatile erosion Walther was the first to describe ventifacts and Dreikanter The form of sand grains gave him indications of their aeolian origin, an approach that was systematically utilized by Andre´ Cailleux in the 1930s Walther dealt with the phenomena of fossil deserts, which he classified as tropical, coastal, plantless volcanic, rain-shadow, and glacial deserts The fact that the different types could be associated with younger or older sediments from other climatic zones was explained by changes in the Earth’s axis of rotation With this idea, he was well ahead of his time In a special publication, Walther described the fauna of a lake in the Buntsandstein desert in Thuringia (1904) From his study of the Nubian Sandstone in Egypt he became convinced of the desert character of the Buntsandstein His ideas about the formation of (minor) salt deposits are still accepted, along with Ochsenius’s bar theory Walther was the first to describe laterite profiles in the deserts of Western Australia, interpreting them as weathering products of a former climate (1915) A revised and enlarged version of his first desert book was published in 1900 and went through four editions until 1924 The last edition has recently been translated into English with commentary (1997) This book was the main reason for his being invited to Australia by the British Association for the Advancement of Science in 1914 In Germany, he was called Wuă sten (desert) Walther National Education The nineteenth century was a golden age for national science education and Walther’s teacher, Haeckel, was indefatigable (and extremely successful) in this field Walther himself wrote a flowing, somewhat poetic, prose, which was very apt for such work His books for a broader public enthused more than one generation and were popular with both school teachers and their students The Vorschule fuă r Geologie (1905) (Elementary Course in Geology), for example, sold 22 000 copies and was translated into Russian and Czech Its last Russian edition appeared as late as 1940 Another successful book was the Geologie von Deutschland (1910) Walther saw an important task in the training of schoolteachers in geology and held many vacation courses for them