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of slender and delicate fossils, of the genus Graptolites and allied genera, found in the Silurian rocks. They belong to an extinct group (Graptolithina) supposed to be hydroids.

A genus of Silurian fossil corals; the chain corals. See Chain coral, under Chain.

A fossil coral of the genus Heliolites, having twelve-rayed cells. It is found in the Silurian rocks.

One of the Invertebrata. Age of invertebrates. See Age, and Silurian.

poda, and Illustration in Appendix. Lingula flags (Geol.), a group of strata in the lower Silurian or Cambrian system of Wales, in which some of the layers contain vast numbers of a species of Lingula.

A series of strata in the lower Silurian formations of Great Britain; -- so named from Llandeilo in Southern Wales. See Chart of Geology.

A subdivision of the British Upper Silurian lying below the Old Red Sandstone; -- so named from the Ludlow, in Western England. See the Chart of Geology.

A genus of spiral gastropod shells, often of large size, characteristic of the lower Silurian rocks.

A subdivision of the Niagara period in the American upper Silurian, characterized by the formations known as the Oneida conglomerate, and the Medina sandstone. See the Chart of Geology.

A subdivision or the American Upper Silurian system, embracing the Medina, Clinton, and Niagara epoch. The rocks of the Niagara epoch, mostly limestones, are extensively distributed, and at Niagara Falls consist of about eighty feet of shale supporting a greater thickness of limestone, which is gradually undermined by…

A Silurian fossil, formerly supposed to consist of eggs.

Of or pertaining to a division of the Silurian formation, corresponding in general to the Lower Silurian of most authors, exclusive of the Cambrian. -- n.

ertaining to, certain beds, chiefly limestone, characteristic of the latest period of the Silurian age. Oriskany period, a subdivision of the American Paleozoic system intermediate or translational in character between the Silurian and Devonian ages. See Chart of Geology.

der division of geological time during which life is known to have existed, including the Silurian, Devonian, and Carboniferous ages, and also to the life or rocks of those ages. See Chart of Geology.

A genus of extinct Paleozoic brachiopods, often very abundant in the Upper Silurian. Pentamerus limestone (Geol.), a Silurian limestone composed largely of the shells of Pentamerus.

A genus of trilobites found in the Silurian and Devonian formations. Phacops bufo is one of the most common species.

Of or pertaining to the lowest beds of the Silurian age, corresponding to the Acadian and Potsdam periods in American geology. It is called also Cambrian, and by many geologists is separated from the Silurian.

roups into which the rocks of the Canadian period have been divided in the American Lower Silurian system. See the Chart of Geology.

t. The saliferous beds of New York State belong largely to the Salina period of the Upper Silurian. See the Chart of Geology.

The period in which the American Upper Silurian system, containing the brine-producing rocks of central New York, was formed. See the Chart of Geology.