Medina rises near the north-eastern foot of St. Cathe rine's Hill, and runs in a narrow valley till near Gatcombe, where the valley becomes wider; it then passes through the chalk ridge near the centre of the island, and flowing on the east side of Newport, forms immediately below the town a wide :estuary, and enters the sea five miles to the north, between East and West Cowes. The Eastern Yar, or Brading River, has its source iu the same range of hills as the Medina, not flu• to the east; it runs in a direction generally north, north-east, and east, and passing through a narrow chasm in the chalk range between Bradiug and Yaverland, then forms Brading Haven, which at high-water is a beautiful lake of 800 acres, but at low-water is a surface of muddy sand traversed by the Yar. The Western Yar rises near Freshwater Gate, and falls into the sea at Yarmouth ; it is an aestuary in nearly its whole length, which is less than three miles.
whole of the strata which compose the Isle of Wight are exhibited in its precipitous eliffa in the most distiuct and eourplete manner. Some of the phenomena which those strata present are extremely curious. The north side of tho island consists of the strata above the chalk ; the centre and the upper part of the south aide consist of the chalk; and the lower part of the south and south-east sides consist of the strata below the chalk. The series above the chalk belongs to what has been called the chalk basin of the Isle of Wight, the boundaries of which are—near Winchester to the north, near Carisbrooke to the south, Brighton to the east, and Dorchester to the west. This basin is circumscribed by chalk-hills, except where it is broken into by the Soleut Sea.
The most extraordinary circumstance in the geological structure of the Isle of Wight is the vertical or highly-inclined position of the central chalk ridge, and of the plastic clay and London clay to the north of it. The strata farther to the north and to the south are horizontal, or nearly so, those to the south being the chalk and under lying strata, which remain undisturbed, while those to the north are more recent formations deposited horizontally and unconformably on the broken edges of the vertical strata. Two great sections of these vertical strata are exhibited by the Culver Cliff and the cliffs of White cliff Bay on the east, and by the Needles Cliff and the cliffs of Alum Bay on the west. In Whitecliff Bay the plastic clay and sands form two low cliffs perfectly vertical; rounding the cape to the south, the chalk of the Culver Cliff rises to a great height at an angle of about 70% dipping north-north-east, and gradually diminishing to about 50'. In Alum Bay a section, quite conformable, hut morn exten
sive and distinct, is exhibited. On the south are the lower strata of chalk and chalk-marl at an angle of about 50' north-north-east, the upper strata of chalk at an angle of about 70'; farther to the north, the plastic clay and its sands, perfectly vertical; still farther to the north, the London clay, also vertical ; and, farthest, a bed of yellow sand inclined at an angle of 60° or 70° north-north-east The face of the chalk ridge is about one-fourth of a mile wide. The upper strata of chalk have alternating strata of flints in a very extraordinary state, the pieces of flint, though closely invested with the chalk and perfectly retaining their forme, being found, when taken hold of, to be shivered into fragments of every size from three inches to an impalpable powder, and the fractured edges of every particle being quite sharp, as if the effect had been occasioned by a blow of inconceivable force. The plastic clay in Alum Bay consists of clays, marls, and sands in a count less number of layers, some extremely thin, of every variety of colour, and most of them, especially when recently cut, singularly bright, like the stripes of a ribbon or the streaks of a tulip. It contains also eight beds of wood-coal, or rather bitumenised wood, each about one foot thick, and vertical, like the other layers. The cross fracture of the coal is earthy; it burns with difficulty, with little flame, and a sulphu reous smell. The line along which the disturbing force acted that occasioned the vertical position of the strata may be traced as far as Abbotabury in Doraetahire.
Another very curious circumstance in the stratification of the Isle of Wight is that of a marine deposit between two fresh-water deposits. This is distinctly shown in a natural section of Headon Hill, on the north side of Alum Bay. Hence it has been concluded that this bill must have been twice the bottom of a fresh-water lake, and at an intermediate period have been covered by the sea. This marine deposit does not seem to be a part of any extensive formation; it only forms a bed of which the actual bouudaries are unknown; but the fresh water formations have been found to correspond very closely with the calcaire greasier of the Paris basin. Beneath these formations in }leaden Hill, and extending into Alum Bay, Totland's Bay, and Cell a ell Bay, is a stratum of pure siliceous sand without shells, from 30 to 50 feet thick, which Is extensively used for making the beat kinds of glass. The whole of the north side of the island is considered to belong to these formations.