The formations already noticed occupy the whole of the county south and east of a line drawn westward from the Berkshire border, three miles south of Highworth, parallel to and a little to the north of the Wilts and Berke Canal, by Stratton to Wootton-Basset and Soend, to the Somersetahire border at Coreley near Frome ; the whole line making a circuit convex to the north-west Beyond this boundary the strata of the middle °elites, comprehending the coral rag and calcareous grit, and the Oxford clay, crop out, occupying all the northern border of the county, and extending westward to a line drawn south by west from Cirencester to Gloucestershire, by Malmesbury, Chippen ham, Melksham, Trowbridge, and North Bradley, to Frome in Sonser setahire ; beyond which lino the upper beds of the lowermost division of the oolites appear.
The tract occupied by the middle oolites has a breadth of eight miles along the northern part of the county, where it extends into Glouces tershire : between Wootton-Basset and Cirencester, it is 11 or 12 miles broad ; thence diminishing towards the south and south-west, so that near Westbury and Frome it is probably not more than one or two miles broad. The lower or outer edge of the coral-rag and calcareous grit may be traced by a range of low bills of this formation, extending to the north of Highworth, Swindon, and Wootton-Basset, and then westward by Lynebam, Bremhall, Bowood, and Brombam. Near Seend, west of Devizes, there is a depression in these hills, through which the Kennet and Avon Canal passes; but the bills re-appear at Steeple-Ashton, beyond which the coral-rag is covered by the westward extension of the chalk and greensand. The average height of the coral-rag hills scorns to be about 400 feet above the level of the sea. The Oxford or chinch clay occupies the lower ground at their foot, including the valley of the Thames, and that of the Avon above Malmesbury. There are some gentle eminences of Oxford clay between Cricklade and Malmeebury, and again about Melksham, Semington, and Trowbridge. Mineral waters occur in this formation; those of Melksham, and of Holt, three miles south-west of Melksham, are im pregnated with purgative salts; those of Seend near Devizes contain iron and carbonic acid. The formations belonging to the lower oolites in this county are the cornbrash, tho forest-marble, then a bed of clay, in some places 80 feet thick, and then the great oolite.
//jedespearpie mad Coneoteicathesse—The county is comprehended In th. three leans of the Thames. the Severn, and the Christchurch or eslisbury Avon ; that part of the south-western border about Stour Load and Mere which Is drained by the Dorsetehire Stour being included in the basin of the Avon, with which the Stour nnites in t laristchurth haven. The northern chalk district and the northern
pert of the county, as far as a line drawn from the neighbourhood of Swindon to near Tetbury in Glonoesterahire, are included in the basin of the Thames; the southern chalk district, with the greensand district whiob begirds it, the Vale of Powsey Best of Devizes nod Market Lavington, and the Vale of belong to the basin of the Salisbury or Christchurch Avon ; and the western side of the county, nearly as far south as Warminster, belongs to the basin of the Severn.
Some of the streams which join the Thames in the upper part of Its course rise in this county. One, which has been considered by some persona. but with very little reason, as the true Thames, rises just on the border of the county where the Hornets road Akeman or Acmau Street crown the Thames and Severn Canal by Thames-head' bridge ; it joins the Churn or true Thames [ntters] from Cirencester, about a mile above Crickisde bridge. This pseudo-Thames has a course of about nine miles before joioing the true Thames. From Cricklado bridge, where the true Thames first touches the county, it flews four miles by Castle Eaton to the border of the county; then between three and four miles farther along the border, separating Wiltshire from Gloucestershire; and quits the county altogether a little above Leoblade. The Key (otherwise the Ray) rim' in the greenssnd hills near Wroughton ; it runs northward, puling to the west of Swindon, and joins the Thames between Cricklade and the border of the county. The Cots rises near Chisledon, and flows northward, chiefly on the border of the county, which it separates from Berkshire, and flows into the Thames just beyond the border of the county.
The moat important feeder of the Thames in this county is the Kennet, which rises In the greensand district near its outer edge, in Cletvaney-fields between Clitle-Pypard and Ystesbury. It flows south and south-east by Vateabury and Avebury, to Silbury Hill on the Bath road, near which it turns eastward by East Kennet, Manton, Marlborough, 3lildenball, and Chilton-Foliat, just below which it touches the border of the county, which it separates from Berkshire for about a mile or a mile and a half, and then, at Hungerford, quits it altogether. That part of the course of the Kennet which belongs to Wiltshire is about 20 miles lone.