Page:A Treatise on Geology, volume 1.djvu/243

 CHAP. VI. the Mendip Hills the distribution of the lias is intricate; south of that chain of limestone, the lias runs out westward between the rivers, and even extends beyond Watchet; from Langport and near Taunton it turns south and (resting on red marl) it passes under the over-extended strata of green sand and chalk. An extraordinary patch of lias occurs in the red marl between Whitchurch and Wem.

Within this long range the lower or Bath oolitic formation is equally continuous, except where unconformable covered by the chalk between the Yorkshire Derwent and the Humber, and in Dorsetshire; and its course may be described as parallel to, and lying on, the eastern side of the lias. Guisborough, Coxwold, Whitwell, South Cave, Lincoln, Grantham, Uppingham, Northampton, Banbury, Stow, Cheltenham, Stroud, Marshfield, Frome, Yeovil, Ilchester, and Bridport, are situated near its western boundary. Parallel to this, and more to the east, is the less continuous range of the coralline oolites, which passes from Scarborough due west to Hambleton, then turns south-east to Malton, beyond which it is concealed beneath the chalk. The argillaceous part of this group (Oxford clay) reappears in Lincolnshire, near Brigg, and passes by Sleaford, Peterborough and Bedford, to Ottmoor near Oxford. From this point the oolitic rocks are added to the series, and the formation fills the vale of Isis to Cricklade, turns south to Chippenham, Calne, and Melksham, and, with some interruption in the oolites, continues by Wincaunton and Sturminster toward Ilminster, where it is covered by the Dorsetshire chalk, but reappears on the south side of it about Weymouth. The Portland oolite formation, represented only by the Kimmeridge clay, fills the vale of Pickering in Yorkshire, borders the chalk and lower green sand of Lincolnshire, from the Humber at Ferraby to Spilsby; underlays a large part of the Fens, and with the Portland oolite fills a considerable breadth in the vale of Aylesbury. Irregularly capped by the same oolite, and sands, the Kimmeridge clay passes by Shotover, Cumner Hurst, Faringdon,