It was the presence of the boulder clay, with its thickness and its ability to be watertight when 'puddled', which persuaded the National River Authority (Anglian) to present a feasibility report in 1993 for a reservoir to be built at Great Bradley. But after opposition from all the local villages this proposal was rescinded in September 1995.

Beneath the boulder clay which dominates the area lies the chalk. This was originally quarried where it came to the surface, and was either burned to produce agricultural lime which was used as a top dressing or was mixed with sand, quarried locally, for mortar used in building. Clay lump was another use of boulder clay, and wattle-and-daub cottages had to be protected by a coating of lime plaster produced from the chalk.

Generally, the most important necessity for living, and the one which often decided the site of a village, was water. Thurlow was probably no exception. It must have been sited where it is for two reasons. First, it was close to the river, which was likely to have been drinkable during the initial settlement; and secondly, the river here was shallow enough for people to cross, as it still is today. It is probable that the two villages of Great and Little Thurlow grew round two main families, who occupied the sites of both Great and Little Thurlow Hall but wished to live separately.