Abstract
Summary The two zones of the Middle Lias of the Dorset coast are remarkably different. The spinatum Zone at the top has a maximum thickness of only two feef, consisting of ferruginous sandstones or limestones containing species of Pleuroceras . The margaritatus Zone is more than two hundred times thick, consisting of loams, clays and sands, wit hard sandstone and limestone bands, containing species of Amaltheus and Amauroceras . In the palaeontological section of the paper, remarks on the amaltheid ammonites are confined to their stratigraphical distribution, and more detailed treatment is given to representatives of Metacymbites, Dactylioceras , and the Middle Liassic hildoceratids Leptaleoceras and Paltarpites . Finally, a comparison is made with the stratigraphy and ammonite faunas of the Middle Lias on the Yorkshire coast, and the conclusion is drawn that differences between the two areas were greater in spinatum Zone times than in margaritatus Zone times.
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