Tropical Forests and Seas
Early – Late Carboniferous (335 to 300 million years ago)
Scotland remained in equatorial latitudes, and the Midland Valley was a very small part of a huge, continental-scale, low-lying coastal plain which had a range of constantly changing landscapes. Usually, it was almost completely covered with luxuriant tropical rainforests. The trees of this time were very different to their modern relatives and only a few were woody, but many were buttressed by having tough bar. Carboniferous trees were simply constructed, small and rapidly growing. As this vegetation died and began to rot it formed thick layers of peat which are now preserved as coal seams.
These Carboniferous peats were like modern blanket bog and raised peat bogs which need regular rainfall to grow. Whereas the more recently formed East and West Flanders raised peat mosses are up to six metres in height, their Carboniferous cousins reached 10 – 22 metres. Between peat bogs, meandering rivers deposited sand in their channels and silt on their floodplains. Organic-rich muds and bog iron ores formed in some small lakes.
Peat accumulation stopped when the coastal plain became submerged under the sea or by large lakes, which drowned the bogs. We know about these floodings because of the many marine and non-marine shell beds preserved in the rock record. Limestones were deposited in clear tropical seas where corals and sea lilies thrived. The drowning was sometimes caused by a global rise in sea-level or climate change, and at other times by land subsidence created by tectonic processes such as earthquakes. Other causes such as wild fires also stopped peat from forming. Over time, delta plains extended out into the sea with wide interlinking channels and lagoons. As the new delta surface emerged as dry land, soils developed as vegetation established anew.
And on to the Tertiary (300 to 2.4 million years ago)
Earth movements at the end of the Carboniferous caused uplift, folding and faulting and halted the sedimentary record in the Lomond area. From the Permian some 250 million years ago to the beginning of the Quaternary around 2.5 million years ago Scotland was carried northwards, from equatorial to temperate latitudes, by continental drift. During the Permian and Trias, the landscape formed under desert conditions with sandstorms. A few volcanoes remained active. In the Jurassic, the climate became humid and warm and later Cretaceous sea probably flooded the area to lay down a veneer of Chalk, which was later completely dissolved and eroded. In the Palaeogene and Neogene (60 – 2 million years ago), the climate cooled and extensive weathering and erosion took place. The framework of the present river systems was also established, only to be changed later by the erosive power of ice.