In large parts of Greater Lincolnshire the older rocks are overlain by deposits formed during the cold and warm periods of the Pleistocene Ice Age.
During a glaciation the rocks beneath the ice were ground to a powder, whilst harder rocks and those falling onto the ice were carried along until the glaciers melted. The materials left behind were a mixture of clays, sands and larger stones, previously called boulder clay, but now named glacial till. Large boulders called erratics were brought from great distances and left behind during the melting. The Millennium Stone at Sudbrooke near Lincoln is an example of an erratic from North Yorkshire. On the other hand much of the till has many fragments of chalk in it, which was eroded locally.
At the end of the last cold stage, very fine sand was picked up by the wind from in front of the ice sheet, and blown across large areas of the northern part of Greater Lincolnshire. These are known as cover sands and were trapped by the ridges formed by the ironstone and the Lincolnshire Limestone. These sands are quarried for glass manufacture and foundry sand.
During the advance and melting of the ice sheets, new rivers were formed and existing rivers were often diverted. The River Trent flowed to the North Sea at different times via gaps in the Lincolnshire Limestone ridge near Ancaster and Lincoln; routes are marked by extensive sand and gravel deposits which have been quarried for aggregate. At Welton le Wold there is evidence for man living in Greater Lincolnshire during one of the warmer interglacial periods.
Melting of ice sheets about 10,000 years ago raised sea levels worldwide, flooding the forests along the Lincolnshire North Sea coast, blocking rivers, and forming the peat and silts in the Fens and the coastal marshes to the east of the Wolds.