SILURIAN PERIOD (445,2-419,2 Ma)
From the Celtic tribe of the silures in the south of Wales.

Main events: first vascular plants.

Lifeforms: on the continents there were small plants with vascular tissue and the first terrestrial arthropods appeared. In aquatic environments, graptolites and some cephalopods were predominant organisms and the fish with jaws and fish with skeletons diversified.

Paleoenvironment: the continental plates of Siberia, Laurencia, Baltica and Avalonia began to approach, and the surface area occupied by oceans was reduced.
The continents were large areas of bare rock, where there were no forests or meadows. In the area of the current Pyrenees, euphoric marine conditions (anaerobic and reducing) occurred.

Cobblestones: not technically feasible (commercial concrete).