424 STKATIGKAPHICAL GEOLOGY 



freestone " (an oolite from 4 to 27 feet thick) and a coral bed 

 occurring at Dundry, Midford, and Stroud (6 to 8 feet). 



The Fuller's Earth which succeeds the above is a marly clay, 

 generally of a greenish or yellowish grey, but sometimes blue, and 

 some of its beds consist of the fine soft greasy clay which is used 

 for fulling purposes. It also includes a band of earthy limestone 

 which is known as the Fuller's Earth Rock. This rock is thickest 

 in Somerset, where it is often from 25 to 30 feet thick. Its 

 characteristic Ammonite is Coeloceras subcontractum, and other 

 common fossils are Ostrea acuminata, Rhynchonella varians, and 

 Waldheimia ornithocephala. 



No limestone comparable to the Great Oolite is found in 

 Dorset or Somerset, so that it must either be represented by the 

 upper part of the Fuller's Earth or strong current must have 

 prevented the accumulation of any sediment for a time. 



The Forest Marble consists of shelly and flaggy limestones, which 

 show much oblique current bedding and alternate with bands and 

 layers of shaly clay or marL It was formerly supposed to be over 

 400 feet thick, but Mr. Woodward has found this to be a mistake ; 15 

 on the coast near Bridport it is only about 80 feet thick, and its 

 greatest thickness is not in Dorset but in Somerset, near Sherborne, 

 where it is about 130 feet. The limestones have been quarried at 

 many places for building and paving stones. 



The Cornbrash in Dorset and Somerset is from 15 to 25 feet 

 thick, and consists of rubbly ferruginous limestone of a bluish-grey 

 colour in its deeper parts, but weathering into a brown rock by 

 oxidation of the iron, and forming a fertile soil (for fossils see 

 p. 417). 



In Gloucestershire the Parkinsoni zone has been divided into 

 two sub-zones or hemeree as Mr. Buckman calls them : (a) the Upper 

 Trigonia Grit or garantiance hemera, consisting of hard earthy and 

 shelly limestones with Trigonia angulata, T. costata, and Ehynch. 

 spinosa ; (b) the Clypeus Grit or Truellii hemera, comprising marly 

 oolites with Clypeus Ploti, Nerincea Guisei, and Terebratula globata. 

 The combined thickness of these beds is about 20 feet near Stroud, 

 but 40 feet on Cleeve Cloud near Cheltenham. 



The unconformity of the Upper Trigonia Grit and the manner 

 in w r hich its base passes across the outcrops of the underlying beds 

 has been described on p. 421, and illustrated by Fig. 141. 



The Fuller's Earth is traceable through the district, but thins 

 northward. Near Stroud it is about 70 feet thick, but not more 

 than 50 near Ched worth, where it passes up into the beds which are 

 known as the Stonesfield slate ; these are shales and laminated 

 micaceous sandstones, which are thin in Gloucestershire but become 



