March 1. The Ordovician begins.

As we discussed a couple days ago, for about 50 years in Britain, where the work was done that laid the basis for much of modern geology, the early part of the Paleozoic era was the Cambrian and the Silurian Periods. Not until 1879 was the controversy about the boundary between them settled, by establishing another period, the Ordovician.

Charles Lapworth named it for the Ordovices, an ancient Celtic tribe that lived in North Wales. They were conquered by Roman Governor Julius Agricola in AD 78-79.

The Ordovician was the last of the major periods of geologic time to be named. There was an analogous controversy brewing in the United States over much of the same time as the Sedgwick-Murchison squabble in England, beginning in 1842 when Ebenezer Emmons described the Taconic System. It’s been called the greatest controversy in American geology, and we’ll talk more about that toward the end of March, but one consequence in the United States was that the U.S. Geological Survey didn’t fully accept the designation “Ordovician” until 1903.

—Richard I. Gibson