At Woburn, Leighton, Ampthill, Sandy, Upware, Wicken and Potton, near the base of Upper Neocomian ironsands, there is a band between 6 in.
The Lower Greensand phosphates have been worked, under the name of " coprolites," at Potton in Bedfordshire and at Upware and Wicken in Cambridgeshire.
From Woburn through Ampthill to Potton a more elevated tract is formed by the Lower Greensand.
At Potton, phosphatized nodules may be obtained, and here a hard bed, the "Carstone," lies at the top of the formation.
Potton (2033), Shefford (874), and Woburn (1129) are lesser towns, and local centres of the agricultural trade.