Geology Of South Downs?

Question

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Answer 1

The South Downs are an east-west trending line of hills that lie just north of the coast of SE England. They are made of chalk (a very fine grained pure white limestone), composed of the microscopic fragments of quite literally billions of algae fossils. The rock is of late Cretaceous age (about 60 million years old). Although chalk is quite soft, it is not as soft as the underlying "wealden clays", which is why they stand proud as a line of hills.

If you stand on the edge of the South Downs,you'll notice that the steep (scarp slope) of the escarpment faces north, and the gentle (dip slope) faces south. This reflects the geometry of the underlying beds, which dip gently south (with a few exceptions!). If you look northwards over the Weald, on a clear day, you will see the North Downs, where the reverse is true. Here the beds dip north and the scarp slope faces south. This is because earth movements during the Tertiary Era, related to distant tectonic activity that formed the Alps, uplifted what were originally roughly horizontal-lying beds into an elongate dome ("anticline"). Erosion then cut through the anticlinal dome, leaving eroded chalk stumps around the rim, with the older, softer wealden strata exposed as lower-lying land in the middle of the dome. Check out any geological map, and you'll see how the outcrop pattern reveals an exhumed dome.

The chalk itself is very porous and permeable, so you won't find any natural water courses on top of the South Downs, as the water seeps through (re-emerging as water springs at the foot of the hills). The numerous valleys (with the exception of the big river valleys that cut right through - the River Arun, Adur, Ouse & Cuckmere) are almost always "dry" i.e. there's no river or stream. The valleys were most likely cut, or modified, at the end of the last ice age, when meltwaters from the retreating glaciers eroded into the frozen chalk permafrost.

There isn't that much good stuff on the web, but I hope this helps!

Answer 2

The rocks of the South Downs, the chalk, is 65-140 million years old. It was formed in the Cretacious Age.

The valleys in them were foreshortened when the sea level rose after the last Ice Age, approx 10-15000 years ago.

Answer 3

The south downs are chalk based hills that were formed in the last ice age if I remember my school geography, if you live near the southdowns the exceat wildlife centre has many books and a table top showing the southdowns and the process of making these amazing geography.