At the end of the period came a time of widespread disturbance, upheaval, and mountain-making, the traces of which are still plain in North America and Europe, especially along the Atlantic slope of each continent. In Nova Scotia and New Brunswick the Silurian strata lie unconformably upon the upturned Ordovician. Along the line between New York and New England the Taconic range was upheaved, its rocks greatly compressed, plicated, faulted, and metamorphosed. Many of the crystalline schists of this region, it has been proved, were derived from the metamorphosis of Cambrian and Ordovician sedimentary rocks. Evidences of this disturbance have been traced as far south as Virginia. The effects of the upheaval were not felt in the northern part of the Gulf of St. Lawrence, for on Anticosti Island the great limestone, which was begun in Ordovician times, continued without a break into the Silurian. The disturbance was along a line of especially thick accumulations as appears from the comparative measurements of the same strata in different areas. The Interior Sea appears to have been entirely drained; at all events no deposits transitional to the Silurian are known from that region.

In the West and Northwest large areas remained land for long periods, but the Interior Sea was soon reestablished in the Mississippi valley. Some narrow strips of land were added to the margin of the Cambrian coasts, and on a line running through southern Ohio, Kentucky, and Tennessee a low, broad arch, the formation of which appears to have begun early in the Ordovician, was forced up by lateral compression. This is called the "Cincinnati anticline or axis".

In Europe the disturbances which brought the Ordovician to a close produced their maximum effects in England, Wales, and the Highlands of Scotland, where the thickness of the sediments is greatest. In these regions the Ordovician beds are folded and often greatly metamorphosed, the Silurian strata lying upon their upturned edges.