GEOLOGY 
Period Formation Character of Strata ap protimate 
thickness in feet 
Alluvium . . River-mud, etc. I-10 
Een Valley Gravels . Gravels of existing rivers 5-20 
River Drift . Older river-gravel and sand 5-10 
Clay-with-flints Reddish clay (on Chalk only) . I-20 
Piciaoeene Brickearth Loam and sandy clay 5-30 
Gravel and sand . 10-20 
Glacial Drift . Boulder-clay with chalk and 
erratics . a 3-100 
Eocene Reading Beds . Plastic clay, loam, and sand ? 10 shown 
Upper Chalk Soft white chalk with vi Sasiges of 
flints . . 100 shown 
Chalk Rock—very hard, cream- 
coloured chalk. : 2-15 
Middle Chalk . . Hard white chalk with few flints 200-210 
Melbourn Rock—hard, nodular 
chalk . . ‘ 8-10 
Grey and white chalk . 2-6 
White blocky and hard grey 
Upper chalk Rie, 60-80 
Cretaceous Lower Chalk ee Stone—hard, si sandy - 
Chalk Marl—grey, marly chalk 70-80 
Chloritic Marl or Cambridge 
Greensand—glauconitic marl ?10 
Upper Greensand . Micaceous and glauconitic sand 0-20 
Upper Gault Variously-coloured clay, part 
sandy, and clayey sand . 25-30 
Lower Gault Light and dark grey sas and 
sandy clay . <3 150-280 
Woburn Sands and Potton Beds 
Lower ‘3 G d —brown ferruginous sand- 
Cretaceous eer eae stone, dark clay, and light- 
coloured sands, rarely green. 230-280 
Kimeridge Clay Dark-coloured clay and shale . 10 
Ampthill Clay . Black clay with bands of lime- 
stone : 40-60 
Upper Jurassic Oxford Clay . Greenish grey and brown clay 300-400 
Kellaways Rock Calcareous grit, shale, and sand- 
stone 10-50 
Cornbrash . . Tough grey limestone and clay 2-15 
Great Oolite Clay. Variegated clays, partly calca- 
reous . ae 5-10 
: | Great Oolite Limestone . | Limestone, marl, ‘and clay . 25-30 
Middle Jurassic Upper Estuarine Series Variegated sandy claysand lime- 
stones 15-30 
Inferior Oolite . . . Northampton Sands — brown 
sandstone and ironstone ?12 
Lower Jurassic | Upper Lias . Blue clay and shale 66 seen 
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