At this time Scotland lay about 10 degrees south of the equator and Laurentia was joined as one landmass to what would become North America and Greenland. Most of Scotland was made up of high mountainous areas of Himalayan or Alpine proportions with a few freshwater basins fringing this super-continent.

Great thicknesses of continental sediments derived from the erosion of the Caledonian Mountains accumulated in internal basins, freshwater lakes and rivers, and in the subsiding Midland valley rift. In Shetland 10 km were formed, 5 km at Caithness and up to 9 km in the Midland valley itself. Associated with these sediments were volcanic lavas up to 3000 meters in the Midland Valley, which probably covered a much larger area than we see today and may have been interconnected with volcanic cauldron subsidence in the southern Highlands. We can imagine a rapidly eroding mountain chain in an arid area with huge volcanoes erupting lava and ash and flash floods washing huge amounts of sediments down into inter-montane basins and lakes. By the end of the Devonian the relief had become low enough for the Rheic Ocean to spread its shallow continental shelf seas over many areas at the start of the Carboniferous Period.
The Devonian period was an important one for the evolution of life. We see the appearance of land plants, marine and fresh-water fish, and towards the end of this period, amphibians. Insects also diversified to include the first winged forms, and so the land and the air were colonised.

One fascinating locality near the village of Rhynie in Aberdeenshire has yielded a unique deposit of chert in which the remains of some of the earliest plants to colonise the land have been found. It is a remarkable example of how early life forms have been preserved in an instant of geologic time. An ancient marsh plant and animal community thrived close to a number of hot springs, which overflowed occasionally and overwhelmed the adjacent area with silica-rich boiling water. This hot solution would cool rapidly and trap animals and plants within it and upon cooling would preserve them. This time capsule of primitive Devonian life has been studies for many years and due to the detailed preservation a lot has been learned about the insects, and plants that lived on the large continent of Laurentia 400 million years ago. The University of Aberdeen has in recent years been looking more closely at this exceptional locality and their website is fascinating and informative. "The Biota of Early Terrestrial Ecosystems: The Rhynie Chert"