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· River Trent at Gunthorpe Lock

Gunthorpe formation
The cliffs on the south side of the River Trent at Gunthorpe weir show a striking geological structure which has taken its name from this location.
Beds of green siltstone and red mudstone are interspersed with layers of crystalline gypsum (Calcium sulphate). The formation has the name 'Gunthorpe formation' and is widespread in Nottinghamshire and Leicestershire. All this material has been mined or quarried, the mudstones for brick clay and the gypsum either for plaster or as alabaster. The gypsum layers vary from wafer thin to approximately 10 cm thick. Most beds are horizontal and essentialyy the same thickness throughout, but in a few layers there is some remarkable splitting and striation of the gypsum beds.

Gunthorpe bridges
Gunthorpe was historically the site of one of the many ferries across the River Trent, but the lack of a fixed crossing between Nottingham and Newark was inconvenient. The presence of villages on either side of the river, and the location approximately half-way between Nottingham and Newark made Gunthorpe an appropriate choice.
The bridge was opened in 1875 following approval of a Parliamentary Bill (necessary to authorise the collection of tolls). As the project was relatively undersubscribed, only a relatively lightweight bridge could be built. limiting the traffic that could be carried. This was nevertheless an improvement on the previous ferry.
With the growth of 20th Century traffic, the bridge was clearly inadequate. The County Council bought out the toll rights and built the present bridge which was opened by the Prince of Wales in 1927. It formed part of a brand new road linking the A46 with the A617, providing a route north for heavy traffic avoiding Loughborough and Nottingham. This was the first instance in the UK of a toll bridge being superseded by a free bridge.