Britain and Scotland united. Devonian 408-362Ma.(Upper Palaeozoic times)
Silurian early Devonian times, approximately 410-380 million years
ago, the Iapetus Ocean had closed causing Laurentia to collide with
Avalonia and Baltica. This continental collision resulted in the
formation of the Caledonide mountains in Scandinavia, northern Great
Britain and Greenland, and the Northern Appalachian mountains along
the eastern seaboard of North America. The collision led to the
deformation, folding and uplift of the Ordovician, Silurian and
older rocks of Northern England, as can be seen most dramatically at
Pettico Wick near St. Abb's Head, Northumberland.
Devonian, a period lasting about 50 million years, fold mountains of
Himalayan proportions, rugged uplands, and intervening basins were
formed over most of Britain. To the south, an ocean called the Rheic
existed, part of its shoreline extending across southern Britain.
It was during
the Devonian period that thousands of metres of rocks were weathered
and eroded away. Although the climate was hot and desert-like,
seasonal rainfall resulting in flash floods led to the deposition of
sands and conglomerates. This resulted in a series of Devonian age
rocks known as "Old Red Sandstone" as opposed to the
"New Red Sandstone" of Permian-Triassic age. Britain would
have been 20 deg. south of the equator, with only limited seasonal rainfall.
The famous unconformity
at Siccar Point,
Ref. NT813710, about 20km SE of Dunbar, discovered by the 18th.
century geologist James Hutton consists of near horizontal Devonian
red sandstones overlying almost vertical Silurian mudstones and
sandstones (greywackes). The
photo above right shows the lady's feet resting on almost vertical
Silurian while she is sat upon near horizontal Devonian (O.R.S.) rocks.