World Paleogeography: Continental positions did not change much in the Early Silurian. But, during the Middle and Late Silurian, Siberia moved north, Laurentia headed southeast, and Gondwana continued to stretch from the Equator to the South Pole. Although it remained almost entirely within the southern hemisphere, Gondwana shifted enough to put northern South America over the South Pole instead of Africa. The massive southern hemisphere glaciers that had formed during the Late Ordovician began melting, and Earth’s climate became relatively stable. By the end of the Silurian, the collision between eastern Laurentia and western Baltica closed the northern part of the Iapetus Ocean and resulted in the formation of a huge mountain range. North American Paleogeography: A shallow sea covered much of North America during the Silurian, except for its southern margin (now the East Coast), which was being uplifted. The uplift began as a collision with an island arc in the Ordovician and developed into a collision with the continent of Avalonia by the end of the Silurian. In the shallow sea, limestones, shales, and sandstones were deposited, and many large reefs developed. Paleontology: The Silurian Period was one of the shorter periods of the geologic time scale. Trilobites, brachiopods, crinoids, and bryozoans were abundant in the shallow seas. Within the Silurian rocks, we find the first coral reefs, which were built by now extinct tabulate and rugose corals rather than the familiar stony corals of modern reefs. Fish were important members of the Silurian fauna. Jawless fishes diversified, and the first fish with jaws appeared. We find the earliest good evidence of life on land during the Silurian: tiny vascular plants that grew in moist areas near the shore and along rivers and streams. Centipedes and scorpions were among the first animals to make the transition to land, and we find their rare fossils preserved in Silurian rocks.