ORDOVICIAN CEPHALOPOD FAUNA OF BAFFIN ISLAND

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Abstract
In southern Baffin Island there are remnants of a limestone and shale formation that was originally quite extensive. A few fossils are known from the western and central portions of this part of the island, and many more from near the head of Frobisher Bay on the southeastern coast. At the last place there is an isolated erosion remnant, Silliman’s Fossil Mount, about three-quarters of a mile long, a third of a mile wide, and 340 feet high. It yields well-preserved fossils in abundance, all of which seem to represent a single marine fauna that is quite varied but is dominantly molluscan and especially cephalopodan. The most conspicuous elements in the assemblage are Receptaculites, Halysites, Calafoecia, Maclurites, Endoceras, Spyroceras, Kochoceras, Lambeoceras, and Westonoceras; but altogether 23 genera of cephalopods are known from the Mount and a considerable variety of corals, brachiopods, gastropods, trilobites, and ostracodes, as well as a few graptolites, bryozoans, echinoderms, pelecypods, etc. Representatives of all elements of the fauna are discussed and (with the exception of the ostracodes) illustrated. The cephalopods are described systematically, as are the trilobites and graptolites, which are treated in supplements by Harry B. Whittington and Charles E. Decker, respectively. Another supplement (by Y. O. Fortier) deals with outliers that are close to Silliman’s Fossil Mount and are of similar composition; and it includes lists of fossils by Alice E. Wilson. The entire assemblage seems to be part of a fauna which is of widespread occurrence in northern North America (including Greenland) and which is known to have extended south to Anticosti Island in the East, northern Iowa in the Midwest, and northern Mexico in the Cordilleran region. It has been best known from the Red River formation of southern Manitoba and the Bighorn formation of Wyoming. In recent years, Foerste, who published extensive studies of this fauna based on large collections from many widely separated localities, correctly interpreted the containing strata as representing a single formation (or group) deposited in a sea which was an enormous epicontinental embayment with Arctic connections. The age of the fauna has long been a moot question. The majority of the species suggest the Trenton, but a not-inconsiderable minority reveal Richmond affinities. It is postulated that the latter are most probably the more significant and that the assemblage is early Upper Ordovician. The abundance and general nature of the fauna, and especially the presence of numerous corals, indicate warm shallow marine waters at the time of deposition.

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