176 FAMOUS GEOLOGISTS/Agassiz Having plate-like scales, often with tubercles or bony points, detached from one another and irregularly arranged on a tough skin (Placoid) Having large, bony, usually shiny (enameled) platelike scales, not normally overlapping, but often interlocking in some way (Ganoid) Having thin, horny, overlapping plates, each having one side with a jagged edge or comb-like projections (Ctenoid) Having thin, flexible, overlapping, horny scales, smooth in outline and circular or elliptical in form (Cycloid) For the Ganoids, Agassiz was especially interested in the modern Lepisosteus, which was the sole surviving modern representative of the group So, like Cuvier (who worked on elephants, mammoths and mastodons), he specifically sought to compare living and extinct types Agassiz’s taxonomic system was later superseded by various others, based principally on bones rather than scales, though his introduction of the Ganoidei was a substantial contribution His taxonomy was problematic, for, while comparing fossilized and modern forms, he saw no evolutionary connection between them On the other hand, he offered something new by the use of fossil fish for stratigraphic purposes Moreover, in a manner that would have appealed to Cuvier, he sought to find out something about the ‘conditions of existence’ of his specimens as to temperature, salinity, and mode of locomotion He supposed that prior to the Cretaceous there seemed to be less distinction between fresh-water and marine forms than at present and it might be the case that these two environments were not so marked previously as they are at present However, Agassiz’s most important contribution to geology was his advocacy of the concept of an Ice-Age (Eiszeit), fundamental to Pleistocene geomorphology and stratigraphy (see Tertiary To Present: Pleistocene and The Ice Age) Curiously, it was linked to the biological ideas that he imbibed from Cuvier In Switzerland, the idea that the country’s glaciers were formerly of greater extent had been recognized by observers back in the eighteenth century, such as the minister Bernard Friedrich Kuhn (1787) There is a report of a manuscript by a mountaineer Jean-Pierre Perraudin (1818), which described the extent of moraines and erratic boulders, and regarded striated and polished rocks as evidence of glacial action It was perhaps Perraudin who really initiated the glacial theory in Switzerland The highway engineer Ignaz Venetz accepted Perraudin’s ideas and read a paper on the topic at Neuchaˆ tel in 1829 The mining engineer Jean de Charpentier, director of the salt mines at Bex, also obtained information from Perraudin and in 1834 read a paper at Lucerne about the former greater extent of glaciers (Agassiz met Charpentier when he was still at school and was partly inspired by him to become a naturalist.) However, Charpentier’s paper was regarded as mistaken and was mocked, Agassiz being one of the opponents (Historians examining Agassiz’s students’ lecture notes from that period have shown that he was then critical of the theory.) But in 1836 Agassiz was in the Bex area and was shown around by Charpentier, and after calling on Venetz and examining the evidences in other parts of Switzerland he became a convert to the theory While in Bex, Agassiz met his old student friend, the botanist and palaeontologist Karl Schimper, and the two also discussed the glacial evidence In February 1837, Schimper gave a botanical talk at Neuchaˆ tel, at the conclusion of which he passed round a copy of a poem that introduced the new word Eiszeit By then, Agassiz had picked up the evidences and ideas in their entirety and was running with them He presented a first outline of his views in public at the meeting of the Socie´ te´ Helve´ tique des Sciences Naturelles at Neuchaˆ tel in July 1837, in what became known as the Discours de Neuchaˆ tel By 1840 Agassiz published his major study on the topic, and his most important contribution to geology: E´ tudes sur les Glaciers In publishing this, he got ahead of Charpentier’s Essai sur les Glaciers (1841), and recriminations followed, stirred up, it has been suggested, by Desor Schimper was also annoyed with Agassiz for failing to mention him in E´ tudes (though he was mentioned in the Discours) There followed a further work on glaciers co-authored with Arnold Guyot and Desor, describing the different types of glaciers, their component parts, their motions, and a detailed account of the Aar Glacier: Syste`me Glaciaire: Ou Recherches sur les Glaciers, leur Me´ canisme, leur Ancienne Extension et le Roˆ le qu’ils ont Joue´ dans l’Histoire de la Terre (1847) The Discours was written in haste, but provided persuasive evidence for the former extension of glaciers, at least in Switzerland, and strong arguments against the floating iceberg theory favoured by Lyell in Britain, or the common idea of glacial erratics being emplaced by catastrophic floods On the other hand, Agassiz thought that erratic boulders might have fallen into their present positions rather than being directly transported by ice Agassiz’s E´ tudes was a sumptuous volume, beautifully illustrated, providing all the documentation necessary to convince readers of the former extension of glaciers The theory could also explain the existence of the vast extent of superficial deposits (‘till’) over northern Europe, then