(a) Of or from the geologic time, system of rocks, or sedimentary deposits of the 2nd period of the Paleozoic Era, characterized by the look of ancient fishes. See dining table at geologic time.
(a) Of a geologic duration within the Paleozoic age; comprises lower, middle and upper epochs from about 488 to 443 million years back.
(a) Of or with respect to a division associated with Silurian formation, corresponding generally speaking to the Lower Silurian on most writers, unique of this Cambrian.
(n) The Ordovician Stage.
(n) from 500 million to 425 million years ago; conodonts and ostracods and algae and seaweeds
(p) The Ordovician duration.
An epithet applied by C. Lapworth to a few rocks not capable of precise separation from those underlying or overlying them, either stratigraphically or paleontologically, but which were the subject of much conversation among English geologists.