So I decided to ask Mr Hobbs , known to many under between the ages of 12 to 18 as "Sir" to explain some whats been uncovered up at the north of the bay.
Geology of the Area
Following the recent storms, a lot of new rock exposures have been uncovered, so here is a rough guide to what Geology we have on the coast north of Swanage Bay.
Swanage Bay is a sandy bay facing east. In the southern part there are low cliffs and banks of Upper Purbeck limestone and shale, these are largely built over and so are not exposed.
To the north there are excellent cliff sections of Wealden strata.
These are the cliffs of soft yellowish and brownish sands and clay with a Coarse Quartz Grit. Lignite and plant debris is common (dark grey/black matter) and dinosaur remains are found occasionally in these Cretaceous fluvial (River) sediments.
Gault clay and Upper Greensand follow as you walk further to the North. Beyond this, where the Purbeck Hills reach the sea is the major Chalk exposure of Ballard Cliff, beneath Ballard Down.
Next to the ravine at Sheps Hollow is a nice exposure of Plenus Marl (Marl is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and silt. This particular Marl looks Blue due to a high percentage of the minerals Glauconite and Chlorite. They are part of the Chalk sequences that make up Ballard down and do contain Chalk / Flint nodules. This Marl would have been deposited in Lacustrine (Lake) conditions.
At the base of Ballard down, the chalk is very fossiliferous and contains various forms of Micraster (Sea Urchin Fossils)
As always, a note of caution, although the Geology is superb in this area, care must be taken.
Landslips are now a very common feature of this part of Swanage and you should also be aware of tide times so you do not get into difficulty.
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