In Europe the Ordovician rocks appear to have been laid down in two distinct seas separated by a ridge of land. The northern area extends from Ireland far into Russia, while the southern is represented by numerous scattered masses. These rocks cover a much wider surface than do the Cambrian. In Great Britain, especially in Wales, they form very thick masses of shales and slates, with but little limestone, intercalated with much volcanic lava and tuff, the volcanic activity being in very marked contrast to the quiet of North America. In Scandinavia these rocks are nearly horizontal limestones and shales, and in Russia they cover very large areas and are so perfectly undisturbed that many are still incoherent sediments. In the southern sea were laid down the Ordovician strata of Bohemia, Germar northwestern and central France, Spain, Portugal, Sardinia, and Morocco.

The very marked difference between the fossils of the two great European areas, and the fact that the Ordovician fossils of other continents agree with those of northern Europe, while those of the southern district are peculiar, indicate that the latter region was a partially closed sea, which occupied the Mediterranean basin, though extending far beyond its present limits.

Asia was largely above water in Ordovician times, but a broad Indo-Chinese sea covered much of the eastern coast, and in northern Siberia are great areas of Ordovician strata, the upper members of which are red sandstones with gypsum and salt. This points to an arid climate. Marine rocks of Ordovician date are found in north Africa, but the equatorial and southern regions are highly peculiar among the continents in the very subordinate part taken by marine rocks of any period, the land being built up almost entirely of continental rocks. In South Africa a thick series of barren sandstones underlies marine Devonian, and probably some of these are referable to the Ordovician. Ordovician rocks are found in New Zealand, Tasmania, and the southern part of Australia. In South America they are not extensively developed, but have been found in Argentina and Peru.

The Climate of the Ordovician, so far as at present known, was uniformly mild and equable, as appears from the fossils of the Arctic lands. No glacial deposits have yet been discovered, though arid conditions obtained in northern Asia.