Fossil Forest, Lulworth Cove, Dorset
East Lulworth has the best-preserved of the fossil forests on the Jurassic Coast. It is not actually the trees that are fossilised, but the circular concretions of the algal burrs which grew around the trees base when the forest floor was flooded. The fossil forest is also seen in several places on Portland and a number of other sites inland from Weymouth
Throughout the Jurassic period, Dorset was on the floor of a tropical sea, and clays, sandstones and limestones were formed on this seabed. Towards the end of the Jurassic Period sea levels dropped and the deposits became exposed to form low-lying land. Soils developed and trees grew. The forest consisted of massive cypress and monkey-puzzle trees that grew alongside giant cycad ferns. Where wood has been found you can actually see growth rings with spacing indicating a variable climate with hot dry years and wetter periods with faster growth.
But soon the sea soon rose again and covered the forest. Algae then grew across the floor of the saltwater lagoon that had engulfed the trees. Mud stuck to the algae, accumulated into many layers, hardened into a thin limestone ring with doughnut shaped structures known as burrs where the trees once stood. This is the fossil forest that we can see today.
One mile east of Lulworth Cove the fossil forest is exposed along a narrow bench in the cliffs. In addition to the trade mark donut shaped algae burrs, the algae have also covered huge fallen logs. Above the forest are the Broken Beds, heaps of jumbled rocks that broke up because of the rapid evaporation of the mineral salt minerals inside them. You can see casts of salt crystals in the rubble around the forest. The forest lies within the Army Ranges and is closed when firing takes place. The ranges are usually open at weekends and school holidays.
Durdle Door is also part of the fossil forest but here the algae have completely grown over the holes where the wood once stood, forming large round structures that are more difficult to spot. A limestone with fossilised ripple marks can be seen in the corner of the bay.
Isle of Portland also has a fossil forest. Here it is exposed along cliff tops and within the quarries. On the east side of Portland Bill, about 300 metres north of the last beach huts, the forest is preserved. Slightly higher up the sequence and just to the south, a bed of ripple marks limestone form a bench on the cliff top. Portland also contains other fossil wood within a massive limestone known as the Top Cap. Thick layers of algae grew around individual trees as they grew, but eventually the trees collapsed and the algae continued to grow over the upper surfaces. The wood has rotted away and what is left are round holes surrounded by strange cauliflower-like growths. One of the best places to view the fossil forest is in the south west corner of the abandoned Kingbarrow Quarry, near the top of the Island and got at from New ground car park.
Devon & Dorset Coast World Heritage Site