is around 100 m thick, suggesting that Dorset remained under water much longer and was robbed of supplies of sand and clay. This bed is composed of fine-grained limestones from white to pale pink in colour. The clearest evidence of fault activity exists in a section of cliff between West Bay and Eype Mouth, where the junction bed thickens in a section of steps, and fractures in the rock contain sediment from the ocean bed, which most likely was sucked in as the cracks opened. The remaining part of the upper Lias is the bright yellow Bridport sandstone of Toarcian age, which gives the cliffs between West Bay and Burton Bradstock their distinctive colour. The sands form a band that runs inland to Yeovil. In the east of the county, these sands are some 900 m below the surface and form the Wytch Farm oilfield's middle reservoir. Inferior Oolite The succeeding Inferior Oolite was deposited in a shallow, tropical marine environment, 35° north of the equator, during the Aalenian to early Bathonian. It is only 2 m thick in the south, but increases to 20 m in the north, near Sherborne. It contains many fossils, including bryozoans, brachiopods, ammonites, belemnites, gastropods, bivalves, and echinoids, and like the previous middle and upper Lias, shows signs of fault-controlled deposition. In some places, the sea floor appears to have been breached, and sediments and fossils were trapped like those in the junction bed between West Bay and Eype. Most of Dorset was starved of sediment, and condensed limestones collected. These limestone beds are often iron rich, lending them a rusty colour. One particular bed, exposed at Burton Cliff, contains large numbers of orange, discus-shaped concretions, which on closer inspection reveal themselves to be pieces of shell from a species of mussel, coated with a thin layer of iron-rich sediment. In the upper section of the Inferior Oolite, two beds are packed with numerous types of sponges, which can be seen around Shipton Gorge and Burton Bradstock. Despite being formed in a marine environment, the oolite, like the lower Lias, contains some fossilised remains of land-dwelling creatures, including two species of Megalosaurus that were found near Sherborne. Great Oolite Fuller's Earth Formation clays were deposited across much of southern Dorset when the continental shelf subsided, forcing the region deeper underwater during the early Bathonian. The lower clays are visible at Burton Bradstock and contain