Prehistory
Originally a river valley, the Solent has gradually widened and deepened for many thousands of years. The River Frome was the source of the River Solent, with three other rivers - the Rivers Avon, the Itchen and Test being tributaries of it. Seismic sounding has shown that when the sea level was lower the River Solent incised its bed to a depth of at least 46 metres = about 151 feet below current Ordnance Datum. The Purbeck Ball Clay contains kaolinite and mica, showing that in the Lutetian stage of the Eocene water from a granite area, probably Dartmoor, flowed into the River Solent.
Seabed survey shows that when the sea level was lower in the Ice Age the River Solent continued the line of the eastern Solent (Spithead) to a point roughly due east of the east end of the Isle of Wight and due south of a point about 3 km west of Selsey Bill, and then south-south-west for about 30 km, and then south for about 14 km, and then joined the main river flowing down the dry bed of the English Channel. Since the retreat of the most recent glaciation the South East of England, like the Netherlands, has been steadily slowly sinking through historic time due to forebulge sinking.
A new theory - that the Solent was originally a lagoon - was reported in the Southern Daily Echo by Garry Momber from the Hampshire and Wight Trust for Maritime Archaeology.
The Isle of Wight was formerly contiguous with the Isle of Purbeck in Dorset - the Needles are the last remnant of this connection.
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