Graptolithus logani was the first fossil named in honour of William Logan, the founding director of the Geological Survey of Canada. Graptolite fossils represent an extinct group of tiny colonial, marine organisms that were found throughout the world's oceans 490 to 385 million years ago during the Paleozoic. Because of their global distribution and their ability to evolve rapidly into distinct forms, graptolites are useful markers used to date Paleozoic-aged rocks.
James Richardson, a Survey geologist hired by Logan in 1846, was the collector of G. logani. He discovered the fossil in the 1850s in the dark shales of the cliffs across the St. Lawrence from Quebec City, near what is today the city of Lévis. Logan entrusted the tiny fossils to James Hall, the New York state paleontologist, who examined and described what were the first graptolites identified in Canada. Specimens of G. logani were unlike graptolite specimens known in Europe or the United States, and their discovery generated much excitement.
The distinct specimens of G. logani have proved to be excellent markers in dating Paleozoic rocks of the Early Ordovician period. The strata where Richardson collected them are no longer accessible because of urban development.
Category: Rocks, Fossils, Minerals and Meteorites
Logan, W.E., 1862. Plan showing the distribution of limestone conglomerates in the Quebec group at Point Levis; Geology of Canada, Multicoloured Geological Map 57; in Logan, W. E., 1865. Geology of Canada. Report of progress from its commencement to 1863. Atlas of maps and sections; Geological Survey of Canada. doi:10.4095/123568