HORTON — GEOLOGY OF THE STONESFIELD SLATE. 
251 
localities, Sevenhampton, near Cheltenham, and Colley Wesion, 
Northaniptonsliirc, is thence denominated Stonesficld Slate. This 
bed of slate, although not exceeding six feet in thickness, is of con- 
siderable local value for roofing-pm^posos ; 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 lamina), 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 
sm'face-ground. 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 planicostatuSj Pleurotoinaria 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 PJioladomija Murcliisoni (?) are abun^ 
dant, associated with a species of Nautilus (N. inflatus ?), Ammonites 
discus, A. Hervcyii, and another species too imperfect for identifica- 
tion ; also Terehratula maxillata, Cardium dissimile, Qresslya perC' 
grina, and Isocardia minima. This pit has also famished some 
interesting sea-urchins, NucleoUtes sinuatus, N. clunicidaris, and a 
few finely preserved examples of Holcctijjms depressus ; also a soh- 
tary specimen of Glijpliia rostmta, 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 
gibhosa, Astarte elegans, A. excavata, Modiola pUcata, M. hipurtita, 
with Tereljratida ohovata, a shell that is very abundant in this locality, 
and highly characteristic of the Cornbrash, and veiy rarely a beau- 
tiful species of sea-urchin, Acrosalima liemicidar aides. The Forest 
Marble derives its name from the adjacent forest of Wychwood, 
