Paleontology and geology
Deposition of limy sediments continued until the end of the Ordovician. At this time, the Iapetus Ocean began to shrink in size, as the crustal plate carrying Europe slowly shifted towards North America. These plate movements were responsible for a mountain-building event called the Taconic Orogeny. As soon as these mountains formed, erosion began to break them down. Rivers carried massive amounts of sediment into the shallow oceans, eventually forming shales and sandstones rich in fossils including brachiopods, bryozoans, and graptolites.