Geology

Paxton Pits only exists because gravel has been quarried here since the 1930s. And the rich layer of gravel is a result of the geological sequence of gravels resting on Oxford Clay. However the events to which the area has been subjected are less simple. A 200-metre borehole, sunk in 1970 across the river in Great Paxton, has enabled geologists to better understand the last 480 million years of local ‘history’. Thanks to John Slack for permission to use information from The Geology of the St Neots Area, available from St Neots Museum.

480 million years ago

The area that is now Paxton Pits was 1000 miles south of the Equator. Huge Himalayan-sized volcanoes, spewing lava and ash, were formed in Scotland and Wales as the continental ‘plates’ were squeezed together. Lower mountains were formed in the area which was later to become St Neots, but in a shallow sea. Alternating beds of sand and mud were deposited on the sea floor, from rivers flowing out of the ‘European’ continent. We know this because marine fossils were found in the Paxton borehole, including trilobites (which browsed on seaweed) and brachiopods (like mussels, which fed on tiny floating life forms). Myriads of worm burrows have been found on the old seabed in rocks that have been identified as from the Middle Ordovician period (about 470 million years ago).

370 million years ago

The ‘European’ continent collided with the ‘Laurentian’ (North American) continent, the join buried deep beneath the modern Scotland/England border during the Devonian period.

300 million years ago

After the collision of continents, the Paxton area was land, but constantly eroded. During the Carboniferous period (300-350 million years ago), there were large swamps to the north and west, which eventually formed coal deposits as plants died.

200 million years ago

During the Permian and Triassic periods (190-290 million years ago), the Paxton area had a hot, desert climate. The mountains were gradually being eroded as the land mass drifted north, over the Equator and across the Tropic of Cancer.

180 million years ago

At the start of the Jurassic period, the land sank and water invaded, to form a shallow tropical sea. The sea’s wave action left a 20 centimetre thick bed of pebbles, called a conglomerate. The pebbles are up to five centimetres in diameter and are now buried 135 metres below Paxton. The climate became wetter and the sea deeper.

This is the period of the dinosaurs; the fossilised remains of some have been found in mudstone near Cambridge. One hundred metres below the modern surface, the remains of mussels, brachiopods, crinoids, belemnites (squid-like creatures) and ammonites have been found.

160 million years ago

The sea becomes shallower, enabling higher land to the south (around London) to emerge. The Paxton area contained low-lying deltas and coastal mudflats, with abundant tropical marine life: sea-urchins, brachiopods and a lobster’s leg have been found. Marine vertebrates, such as the dolphin-like ichthyosaurs, plesiosaurs (long-necked creatures, rather as ‘Nessie’ is supposed to be) and fishes lived in the shallow seas. Their remains have been found in local brick pits and a complete ichthyosaur, found in Little Paxton quarry, is now the Sedgwick Geology Museum in Cambridge.

The remains of these animals have been found in the final layer of Jurassic rock, which took five million years to accumulate, known as Oxford Clay. It is 35 metres thick and stretches in a crescent from modern Dorset, via Oxford and Paxton, to East Yorkshire. It is exposed by quarrying in the Ouse Valley, including at Paxton Pits.

90 million years ago

Sediments from rivers and rocks, including chalk, continued to be deposited in the Paxton area. The remains of invertebrate sea creatures have been found in the top layers of the Oxford Clay.

65 million years ago

Much life on earth, including the dinosaurs and ammonites, was wiped out as a result of a rapid change in climate, believed to be the result of an asteroid hitting the modern-day Gulf of Mexico.

480,000 years ago (The Ice Age)

Ice sheets moved south, burying Paxton beneath several kilometres of ice. For the next 470,000 years, similar ice sheets would expand and contract on at least 14 occasions. Each ice sheet was present for several decades and then retreated for thousands of years. As the ice melts each time, deposits of boulder clay dragged along by the ice, were left in the Paxton area. The landscape looked much like Siberian tundra does today, but as it warmed, plants started to grow.

During these Interglacial periods, the climate was temperate (similar to today, and sometimes warmer) and supported communities of plants and animals. This is when mammoths, woolly rhinocerous and hippopotamus wallowed in the rivers and browsed the trees, while herds of bison, reindeer and horses grazed the lush river banks. The remains of several mammoths have been found at Paxton Quarry. Pollen grains trapped in the teeth of the fossilised animals show us that trees such as alder, arctic dwarf willow and willow grew on the river edges, while sedges and alpine plants (thrift, bladder campions and pinks) formed the diet of the grazing animals.

125,000 years ago (The Ice Age)

During the final Interglacial (known as the Ipswichian), the whole of East Anglia was dominated by a huge river system, as big as the Mississippi is today. Discoveries from Barrington, near Cambridge, indicate that the conditions were tropical, perhaps more like parts of Africa today.

Even the ice sheets which didn’t make it this far south affect the area; the melting ice produced huge volumes of water which washed boulders from the clay deposits, often over great distances. As the flows cease, they leave shingle bars and islands on the floodplain. One such shingle bar is over a mile wide, from Eaton Ford to Eynesbury. This bar caused the meltwater to split into several smaller channels. Gravel was created by the continued erosion of the land surface and was deposited by water in these channels.

>10,000 years ago

As the last ice sheet retreated, the land became drier and the wide channels were replaced by a narrower, meandering river that is the River Great Ouse (though it has occupied several positions across the valley). During the last 10,000 years, the river has cut down into the old floodplain, leaving a record of its successive levels in the form of paired river terraces.

The last 10,000 years

Although there is evidence that people inhabited the area during the Stone Age (the period immediately after the Ice Age), it was the Bronze Age before settlements started to develop. The mud deposits from the river meant that the surrounding land was very fertile, with lots of vegetation that could provide food for roaming people. In time, as hunter-gatherers became farmers, this proved to be a good area to farm, with vegetables growing well in the soils. The river also provided sustenance and a means of transport, though in time, it became polluted and the gravel and sand deposits proved a valuable source of water. A large number of wells have been sunk into the deposits, enabling the neighbouring villages of Eynesbury and the Priory in St Neots to develop.