A hypothetical continent which existed during the Paleozoic Era, Laurussia was formed during the Devonian Period when several fragments of the ancestral supercontinent Rodinia collided with each other, especially
- Laurentia, constituting the core of present-day North America (especially its craton, the Canadian Shield).
- Baltica, the rocks now underlying Scandinavia, the North European Plain, eastern Russia, and Ukraine. The Caledonian Orogeny formed the mountains of Norway, Greenland, Labrador, and parts of Scotland.
- Avalonia, a Japan-like volcanic minicontinent whose rocks now lie beneath the Atlanic Coastal Plain (but whose batholiths poke through as gneiss domes in central Maryland), and also show up in southeastern New England, Down East Maine, Nova Scotia, Newfoundland, Ireland, and Great Britain. This collision caused the Acadian orogeny.
During the Devonian Period, Laurussia was mostly tropical, extending from 30 degrees south of the Equator to just north of it. West of the Acadian mountains was the Kaskaskia Sea, a shallow ocean extending from what is now southeastern New York and central Pennsylvania to large archipelagoes formed by the ancestral Sierra Nevada.
The Acadian Mountains eventually eroded down to a peneplain, but the debris formed sedimentary layers that now form the Catskill and Pocono Mountains of New Tork and Pennsylvania, as well as the Old Red Sandstone of Great Britain. Laurussia was recognized as a paleocontinent when the similarity of these sedimentary rock layers was rcognized. Because of this, Laurussia is often called the "Old Red Sandstone Continent".
In the Mississippian period, Laurussia straddled the Equator from 30o N to 30o S. As the Mississippian Period progressed, limestone layers were being laid down in the shallow Kaskaskia Sea. As time progressed into the Pennsylvanian Period, vast coastal swamps formed on the western slopes of the mountains. In these swamps the coal deposits of the Western Appalachians were laid down. Further east, Laurussia collided with ancient Siberia to form the continent Laurasia. Soon afterward, during the Permian Period, Laurasia collided with Gondwana to form Pangaea.
Most information came from the excellent site, "The Geological Evolution of Virginia and the mid-Atlantic Region", at
http://geollab.jmu.edu/vageol/vahist/index.html