- These are overlain by low-grade metamorphosed sediments and volcanics of Ordovician and Silurian age.
- Because of the disparate nature of the Ordovician and Cambrian records, it is difficult to make direct comparison between the two events.
- In contrast, the Ordovician magmatic event postdates the pre-Variscan deformation in the external zone.
The Ordovician lasted from about 510 to 439 million years ago. It saw the diversification of many invertebrate groups and the appearance of the first vertebrates (jawless fish)
late 19th century: from Ordovices, the Latin name of an ancient British tribe in North Wales, + -ian.
Definition of Ordovician in:
- The US English dictionary