Report on the Geology of the County of Londonderry, and of parts of Tyrone and Fermanagh. [With maps and plates
A geological survey report on County Londonderry and parts of Tyrone and Fermanagh, compiled by Joseph Ellison Portlock for the Ordnance Survey of Ireland and published in 1843 for geologists and mining readers. The 74 plates are finely stippled lithographs of Palaeozoic fossils — trilobites in slab, ribbed brachiopod and bivalve shells, crinoid stems, coral fragments and teeth — numbered and floated on bare paper, useful as isolated line-and-dot specimen motifs.
