406 J. C. Mansel-Pleydell— Geology of Dorset. 



posed of comminuted shells and sandy slates, to wliicli tlie name 

 ■was given by William Smith, in consequence of the large area 

 covered by it in Wychwood Forest. It abounds in ripple and 

 current-marks, from which, and, from the wood it frequently con- 

 tains, it is inferred that it must have been formed in a shallow 

 sea. In Dorsetshire its lowest portion chiefly consists of clay, 

 with occasional layers of thin fissile and sandy limestone. 

 The soil is generally cold and wet, and is mostly confined to 

 pasturage. The limestone is quarried for flagstones and building 

 materials, and in the neighbourhood of Bridport it is burnt for lime. 

 The upper formation of this series, Cornhrash, consists of a loose, 

 Tubbly, fossiliferous limestone, and is useful for road-making and 

 conversion into lime. The most northern position is Stalbridge, 

 where it attains a breadth of three miles, and takes a southerly 

 direction from Purse Caundle to Holwell, where a fault throws it 

 northward towards Haydon ; here it flanks the Honeycombe and 

 Lillington range, passing through North Wootton, Folke, Leweston, 

 to Beer Hackett, where it is again displaced by a fault, and appears 

 once more at Eyme, Tetminster, Melbury Sampford, West Chel- 

 borough, to Eampisham, where it is closed in by the Greensand of 

 that district. It occupies a considerable area in the Vale of Bredy, 

 about eight miles long, and five miles broad, bounded on the north 

 by the overhanging escarpment of the Glial k and Greensand, on the 

 south by the sea and Chesil Bank, and on the west by the Inferior 

 Oolite. It also has a considerable extension in the Vale of Wey- 

 mouth, extending from Langton Herring to Eadipole. Owing to 

 the predominance of phosphoric acid and carbonate of lime, the 

 superiority of the Cornbrash over the Forest Marble in an agricul- 

 tural point of view is well marked. At Puncknoll and Swyre, 

 where the green pastures and brashy arable fields of the northern 

 portion of the parishes are succeeded on the southern side by hard 

 stiff unyielding clays, scarcely repaying the expense of the plough- 

 share, there is no doubt as to the superiority of the Cornbrash for 

 agricultural purposes. Professor Buckman has presented facts in 

 connexion with the distribution of fossils in the Inferior and Great 

 Oolite beds, showing that twenty-one species of Lamellibranchiate 

 bivalve Mollusca, which are common to the Inferior Oolite and 

 Cornbrash in Gloucestershire, are rare or wanting in the Great Oolite 

 of the district. The recurrence of species he considers to be depen- 

 dent on the recurrence of similar physical conditions. 



Oxford CiiAY — is a nearly uniform mass of dark clays and shales 

 with occasional beds of argillaceous limestones : the characteristic 

 fossil is GrypJicea dilataia. It occupies a more extended area than 

 any of the previous beds, and is not so disturbed by faults ; it has an 

 uninterrupted course from Buckhorn Weston, Stalbridge, Lydlinch, 

 Stock, Holnest and Melbury Osmund, about twenty miles in length, 

 and three in breadth. It is flanked on its eastern extension by the 

 Coral Eag at Hilfield, and is overlapped by the Chalk escarpment ; 

 its western extremity, lying at the base of Melbury Bubb, being less 

 regular, owing to the dislocation of the subsequent beds. It appears 



