Winston van Stroong

Brøgger (1901) reports shells of high-arctic shallow-water mollusca dredged from great depths of the Norwegian Sea, implying that the sea floor’s depth below the surface at the maximum of the last ice age’s glaciation, the greatest ice-sheet of Europe, differed from its present depth by at least 2,600 m. The case rests on the depth habits of a single fossil fauna. Brøgger shows that the characteristic species of the older yoldia clay “live in abundance in the high arctic seas only at depths from about 10 to 30 metres,” while their deeper-dwelling arctic neighbours “have never been found in the typical older yoldia clay.” The fauna is therefore a reliable gauge of shallow water. Yet the dredges of the Norwegian North Atlantic Expedition near Spitsbergen and of the Danish Ingolf Expedition between Iceland and Jan Mayen raise “the high-arctic fossil shallow-water mollusca of the yoldia-fauna” from “great depths of the Norwegian Sea,” down to 1,450 fathoms. Animals bound to the shallows lie where no such animal can live. Clays cement the argument, because “the species of shells in question are mostly forms that live on a clay bottom, mostly at 5–20 fathoms.” Brøgger’s footnote also says ice transport would mostly give fragments, “whereas in reality even fragile forms such as Portlandia arctica are found at the great depths as whole valves.” Edward Hull, in 1902, cited the 2,600 m as agreeing with his own estimate of a 1,200-fathom (7,200 feet) difference in the level of Western Europe during the intensest cold of the Glacial period. Brøgger, Om de senglaciale og postglaciale nivåforandringer i Kristianiafeltet, NGU No. 31 (1900–1901) nva.sikt.no/registration/019… Edward Hull “Sub-Oceanic River Valleys,” Geological Magazine (Decade IV, vol. IX, 1902) cambridge.org/core/services/…