Beschrijving
Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Virgilian series is the most recent part of the Pennsylvanian epoch in the North American geologic classification series. In the older Appalachian classification system, this series was known as the Monongahela group. As with other Carboniferous series, it comprises cyclothems, or distinct cycles of sedimentary rock formation. The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly 318.1 ± 1.3 to 299 ± 0.8. As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few million years. The Pennsylvanian is named after the American state of Pennsylvania, where rocks with this age are widespread.