back to Scotland homepage
Our
stops on day four were slightly more geological in nature, while still steeped in the
human history of the region. They included the hot springs and Roman ruins at Bath,
Stonehenge, and the Salisbury Cathedral.
The hot springs that fed the Roman baths at Bath are a geological oddity in the
relatively inactive British Isles. Warm water that would normally stay deep in the crust
has found its way to the surface via an old fault. Humans have used the site for thousands
of years.
There are hardly enough cliffs in southern England to worry about falling rocks, but
the 800 year-old cathedral walls are a different matter.
I am not sure which saint was represented in this carving, but considering the rocks in
his arms, perhaps the patron saint of rock collecters?
The storm drains for Salisbury Cathedral are truly unique.
A quick history of the central part of the British Isles:
An authority on English geology (D.V. Ager) remarks that although much of the geologic
time scale was perceived and organized in England, “We would probably agree that it
would be better sometimes to look elsewhere for standards than in those overgrown ditches
and abandoned quarries that provide so much of our inland geology in southern Britain”.
In general, the Central British Block made a journey during Paleozoic,
Mesozoic and Cenozoic time that began south of the Earth’s equator. The
rocks of the British Isles record the changing climates as the landmass moved from the
equatorial regions through the desert subtropics and into the temperate midlatitudes.
The early Paleozoic rocks record oceanic deposits until the
Caledonian Orogeny, which was caused by a continental collision with the North American
continent. Mountains rose west of the Block, shedding vast amounts of river and alluvial
fan sediments over the former limestones of a shallow sea. The Devonian layers are called
the Old Red Sandstone, and we will see and hear much more about this distinctive
layer in Scotland.
At the end of the Devonian, the mountains had worn away, and
the region was a flat red floodplain. A shallow sea invaded the region, depositing vast
areas of limestone, with fossils of corals, brachiopods, and crinoids recording tropical
conditions near the equator.
In later Carboniferous times coastal swamps and marshes
gave rise to thick coal beds that helped to energize the Industrial Revolution in
England.
At the end of the Carboniferous, mountains began to rise to the
south as Africa collided with Europe. Permian and Triassic sediments show that the
landmass was now under the influence of the arid subtropical belt, and England was a
desert.
In Mesozoic time, the Atlantic Ocean began to form as
Greenland and North America started to pull away from Europe. In the words of D.V. Ager,
“Britain hesitated. It was as if our island home could not make up its mind whether
to go west with brash young America or to stay with wrinkled old Europe. Early in that
opening Wales nearly separated from England in a tentative act of devolution long before
the red dragon, the Welsh language or the game of rugby.”
By Jurassic and Cretaceous time, England was entering
more temperate latitudes, and terrestrial and lake sediments preserved some of the first
dinosaurs to be found and described in Europe. A sea spread over the region, forming among
others the famous chalk layers that created the white cliffs of Dover.
The
final parts of the story are the ice ages that affected northern England during the
last 2 million years. Scotland was engulfed, but southern England remained ice free in
large part. In the last 15,000 years, the ice retreated, and England took its present
shape.