306 JURASSIC. 



Mr. Bristow informs me that at Long Burton in the neighbourhood of Sherborne 

 (Dorset), beds of Forest Marble are sometimes polished for ornamental purposes : 

 this has been called the Yeovil Marble. As a rule, however, it is too much 

 impregnated with ochreous galls to be useful as marble. Slabs of Forest Marble 

 are employed to form the sides of piggeries and cattle-sheds. The smaller pieces 

 broken up form a very durable material for road-making. Some of the thicker 

 blue-centred slabs are used for building-purposes, for which (especially in the 

 shape of rough ashlar) they are admirably adapted, as they readily form even 

 courses of a somewhat regular thickness. As a soil, the Forest Marble is usually 

 poor, but capable of great improvement by draining and cultivation. ^ Some of 

 the flaggy beds are used for paving ; and at Bothenhampton (B'ampton Stone), 

 near Bridport, and other localities eastwards to near Weymouth, the more cal- 

 careous beds have been burned for lime. The Forest Marble is, however, rarely 

 burnt for lime where Cornbrash is readily to be obtained. It is probable that 

 iron-pyrites has originally been the colouring material of the blue bands of the 

 Forest Marble, and that the yellowish-brown exterior is due to the oxidation of 

 the pyrites.* Saline waters have been met with in the Forest Marble at Swindon 

 (well), and other places in Wiltshire.^ 



COENBEASH. 



The Cornbrash, so named by William Smith, consists of pale 

 earthy and rubbly limestones, sometimes shelly, sometimes of a 

 pasty or marly consistency. The beds, where not exposed to 

 atmospheric influences, are compact, blue in colour, and often 

 sufficiently hard to be used for rough building-purposes, as near 

 Malmesbury, and at Radipole, near Weymouth. The thickness of 

 the formation varies from 5 to 40 feet. 



As a rule the formation is very fossiliferous, bivalve Mollusca 

 being most plentiful. The more abundant species are Avicula 

 cchiiiata, Pholadomya hucardium {dcUoidea), Gresslya peregri'na, Myacites 

 securiformis, AI. deairtatus, Wahiheimia {Tercbratula) obovafa, Terebra- 

 titla lagenalis (allied to W. ormthocephala), Rhynchondla concinna 

 and Echinobrissus {^Nucleolites) cluniciilaris. The Cornbrash and 

 Forest Marble have been grouped together as the zone of Tcrebra- 

 tula lagenalis. Ammonites macrocephaliis {Herveyi) is abundant in 

 the Midland Counties, but rarer in the south ; A. disais and Nautilus 

 are also found. Belemnites are not known. Polyzoa occur ; and 

 among other fossils we may mention Ostrea Marshii {flabelloides), 

 O. Sowe7'byi, Lima duplicata, Pecten vagafis, Isocai'dia, Trigonia costata, 

 Homomya gibbosa, Modiola Soiverbyana, Ceromya concent rica, Goniomya, 

 Terebratula intermedia, Rhynchonella Morierei, Holcctypus depressus, 

 Acrosalenia spitiosa, Anabacia orbulites, Bathycccnia, etc. 



Some irregular forms of Ostrea {O. irregularis) are found in the 

 Cornbrash (as well as other formations), which have imitated the 

 forms or markings of different organisms.^ 



1 J. Buckman, Bath and W. of Eng. Agric. Journ. xiii. 



2 A. H. Church, Q. J. Chem. Soc. (a^^ii. 379. 



3 Q. J. xlii. 2S7. ^ Jud'd, G. Mag. 1871, p. 355. 



