1. _The Titterstone Clee Hill_ forms a ridge about seven miles long and a mile and a quarter broad, running in a north-easterly direction over the Old Red Sandstone uplands of the south of Shropshire. The ground rises gradually towards the south-west, until it reaches there a height of 1754 feet (Fig. 232). On the north-western side of the ridge, the last vanishing representative of the Carboniferous Limestone can be seen to be overlapped the Millstone Grit, which, as it is traced towards the south-west, is in turn overlapped by the Coal-measures, and these, about 400 feet thick, then rest immediately on the Old Red Sandstone. Two sheets of columnar olivine-dolerite, possibly originally connected, lie as cakes on the summit and eastern slope of the ridge, and cover in all a space of about a square mile and a half. The larger sheet, which varies from 60 to 180 feet in thickness, overlies the Coal-measures, and the coals of the Cornbrook coal-field have been worked underneath it. The smaller mass, which may be 300 feet in thickness, forms the summit of the ridge. On its eastern side it reposes on Coal-measures, which are there much disturbed; but on the west side, where it forms a bold capping to the escarpment, it is underlain at once by the Old Red Sandstone. There cannot be any doubt that these masses of eruptive material are sills, which have been injected into the Carboniferous strata, and partly between these strata and the Old Red Sandstone. One or more dykes of eruptive rock have been met with in mining, and the coal on approaching them undergoes alteration.[113] [Footnote 113: See J. R. Wright, _Trans. Geol. Soc._ (2nd ser.) iii. (1832), p. 487. Titterstone Clee Hill is shown on Sheet 55 N.E. and N.W. of the Geological Survey, and in Horizontal Sections, Sheets 33 and 36, from which Fig. 232 is reduced. The microscopic structure of the dolerite has been described by Mr. Allport, _Geol. Mag._ 1870, p. 159; _Quart. Journ. Geol. Soc._ xxx. (1874), p. 550.] [Illustration: Fig. 232.--Diagrammatic section across Titterstone Clee Hill. 1. Old Red Sandstone; 2. Carboniferous Limestone; 3. Millstone Grit; 4. Coal-measures; 5 5. Columnar olivine-dolerite.] 2. _Brown Clee Hill_ consists of two outliers of Coal-measures, each about a mile long, placed on the summit of a broad ridge of Old Red Sandstone, and rising to a height of 1800 feet above the sea. Both of the outliers is capped with a cake of dolerite, and a third smaller patch of the same material lies on the southern outlier between the cappings. Neither at this locality nor around Titterstone Clee have any eruptive rocks been observed rising through the older strata. It is evident that in both cases the orifices or fissures up which the molten material rose lie concealed under the surviving cakes of dolerite.[114] [Footnote 114: Brown Clee Hill is mapped in Sheet 61 S.W. of the Geological Survey, and its structure is shown in Sheet 36 of the Horizontal Sections.]