145 to 100 million years ago: Lower Cretaceous

Towards the end of the Jurassic period, Greater Lincolnshire was again covered by a shallow sea with a low lying coastline north of the present day Humber.

The true Lower Cretaceous sequence starts in the southern Wolds with the Spilsby Sandstone, whose deposition started in the final part of the Jurassic period and continued into the Cretaceous. Thinning to the north and east, it is most notable and extensive in the southern end of the Wolds where most of the medieval churches of the area are built of this distinctive dark green to brown coloured stone. Unfortunately many, including Horncastle, are showing the effects of weathering on this not very well cemented sandstone.

Above the Spilsby Sandstone the rocks are mainly clays, but include local areas of limestone near Tealby; the Claxby Ironstone, formerly mined near Nettleton; and the Roach Ironstone. The Carstone, a gritty sandstone that gets finer to the south, follows at the end of the Lower Cretaceous and the start of the Upper Cretaceous.

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