31. More recently two locations in mid Wales have been selected to globally define stages of the Silurian period . 32. The rocks underneath Chisholm are two kinds of volcanic rock that erupted from volcanos in the Silurian period . 33. Acanthodians are a type of ancient fish dating back the late Silurian period , often being called spiny sharks. 34. It lived in the Silurian period . 35. The Devonian Period rocks are more common than Silurian Period rocks, making up two thirds of the county. 36. Over the porphyroids lie various horizontal beds of slate from the Silurian period that are often clayey-sandy on top. 37. The earliest previously known fossil records of land-dwelling creatures date from the Silurian period some 50 million years later. 38. In the 1840s fossils of brachiopods and trilobites from the Silurian period were discovered at Woolshed Creek near Duntroon. 39. These rock formations mainly consist of shales, sandstones, and conglomeratic sandstones that date to the Ordivician and Silurian periods . 40. Fossils ascribed to the Lycopodiophyta first appear in the Silurian period , along with a number of other vascular plants.
