- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
North of Ardagh, southwest Ireland, the Clare black shales at the base of the Namurian (Carboniferous) contain several beds with a preponderance of sponge spicules. The rock is hard and dark gray, with a tendency to split along stylolitic planes, and consists of microcrystalline quartz, argillaceous material, and a fair amount of carbonaceous matter. The spicules are almost exclusively monaxon fusiform oxeas, and are either quartz or chalcedony. The spongolite apparently represents a former localized colony of sponges, but the accumulation of spicules in one place is not readily explained. Comparable material has been found in Belgium, and it seems likely that other occurrences will be found in Ireland.