The original land surface was around above the current sea-level. The surface had sandy deposits from an ancient sea, laid over sedimentary clay (this is the blue London Clay). All the erosion down from this higher land surface, and the sorting action by these changes of water flow and direction, formed what is known as the Thames River Gravel Terraces. Sand and gravel was deposited near Beaconsfield and other places by the ancestral River Thames This sand and gravel is now being excavated near near Beaconsfield.
thE OrIGInal LanD surface waS arouNd aBOve THE CuRRent sea-LevEl. the SUrfaCe hAd sandy dePosIts froM an AnCiEnt Sea, lAid Over sedimentary cLay (this IS tHe blue loNDOn cLay). All the erosion down fROM tHiS HighEr lAnd surFaCE and the sortiNG actIon by THese cHANgEs of waTER flOw and direCtion, FoRMED whAT is knOwn as The ThAmes rIver gravel tERRaceS. SaNd aNd gRaveL was dePosited NeaR beacONsFielD and othEr PlaCes By the aNCeStral RivER tHAmeS THIs Sand aNd GraVEl is NOw beinG ExcaVaTed neaR NeAr BEaConsfield.