HOETON — GEOLOGY OF THE STONESFIELD SLATE. 251 



localities, Seveiiliainpton, near Cheltenliam, and CoUey Weston, 

 ISTorthamptonsliire, is tlience denominated Stonesfield Slate. This 

 bed of slate, although not exceeding six feet in thickness, is of con- 

 siderable local value for roofing-purposes ; and, indeed, all over 

 Oxfordshire more or less of Stonesfield Slate may be observed on the 

 roofs of the houses, churches, and other buildings. It contains some 

 pebbles of a rock very similar to itself, which, as Sir C. Lyell 

 suggests, may have been portions of the same bed broken up and 

 subsequently re-deposited, and when first raised is very compact, but 

 after having been exposed to the action of frost, readily divides into 

 thin laminae, and in that state is dressed with the hammer, and pre- 

 pared for the market. Unlike its equivalent formation in Gloucester- 

 shire, the Slate is not exposed in open quarries, but worked by means 

 of well-like shafts penetrating the overlying Oolitic strata, and vary- 

 ing in depth from thirty to sixty feet, according to the level of the 

 surface-groand. Although the Stonesfield Slate will receive the 

 largest share of our attention, yet these overlying beds, which are, in , 

 descending order, the Cornbrash, Forest Marble and Bath Oolite 

 demand a brief notice that perhaps will not be deemed out of place. 

 Below the Stonesfield Slate a ferruginous bed of Inferior Oolite may 

 be observed at the base of the hill in the adjoining parish of Fawler, 

 This, since the time of its discovery (February, 1859), has been 

 largely quarried for iron-ore, and found to contain a considerable per 

 centage of that metal. At a distance of about four miles from 

 Stonesfield, in the same direction, near Charlbury, the Lower Lias 

 was exposed some years since by a cutting of the Oxford, Worcester, 

 and Wolverhampton railway, and yielded some beautiful specimens 

 of Ammonites plmiicostatus, Pleurotomaria Anglica, and other Liassic 

 fossils. 



The Cornbrash presents itself in this district as a hard, coarse, 

 flaggy limestone, with thin bands of brown marls and clay, and when 

 in a state of decomposition furnishes a valuable soil for agricultural 

 purposes. It may be studied to advantage in the neighbourhood of 

 Witney, more especially at a quarry on the side of the Woodstock 

 road, where fine specimens of Pholadomya Murchisoni (?) are abun* 

 dant, associated with a species of Nautilus (N. inflatus ?), Ammonites 

 discus, A. Herveyii, and another species too imperfect for identifica- 

 tion ; also Terehratula maxillata, Cardium dissimile, Gresslya pere- 

 grina, and Isocardia minima. This pit has also furnished some 

 interesting sea-urchins, Nucleolites sinuatus, N. dunicularis, and a 

 few finely preserved examples of Holectypus depressus ; also a soli- 

 tary specimen of Glyphia rostrata, a crustacean allied to the lobster. 

 In addition to the above, from some shallow openings on Curbridge 

 Common have been collected Trigonia costata, T. impressa, Lima 

 gibiosa, Astarte elegans, A. excaData, Modiola pliccda, M. hi/partita, 

 with Terehratida ohovata, a shell that is very abundant in this locality, 

 and highly characteristic of the Cornbrash, and very rarely a beau- 

 tiful species of sea-urchin, Acrosalinia hemicidaroides. The Forest 

 Marble derives its name from the adjacent forest of Wychwood, 



