Silurian Period, a division of geologic time that began about 444,000,000 years ago and lasted about 35,000,000 years. It is the third period of the Paleozoic Era, coming just after the Ordovician Period and just before the Devonian Period. The Silurian Period is named after the Silures, an ancient people who lived in Wales, where rocks of this period were first studied.
Climate during the early Silurian Period was mild over much of the earth. Large shallow seas covered large portions of the continental land areas. Shales, limestones, sandstones, and conglomerates and quartz-ites were widely deposited. Toward the end of Silurian times the seas began to dry up, leaving many salt deposits where their shores had been.
Great Silurian rock formations are found in Pennsylvania and New York State and surrounding areas. Other extensive Silurian deposits are found in Great Britain and in the Czech Republic. Salt, iron, and some gas and oil are recovered from Silurian rock formations.
Animal life in Silurian times included primitive mollusks, sponges and corals, brachiopods, and early crustaceans such as trilobites.