TABLE OF FORMATIONS Era or Group Period, or System Formation Character of the strata in Northamptonshire Approximate maximum thickness in feet Recent Alluvium .... Dark carbonaceous mud or loam . IS Quaternary or Post- Tertiary Recent and (or) Pleistocene Fen-land .... Valley Gravels . . Gravels, sands, clays and peat . Alluvial gravels and sands . . . ? 35 Pleistocene Upper Boulder Clay . Mid-glacial Gravels . Lower Boulder Clay and Sands Clay, with much chalk and many erratics Coarse gravel to fine sand . . . Gravels, sands, loams and clays ; few erratics 100 35 170 Cainozoic, or Tertiary Pliocene, Oligocene, Eocene (absent) Upper Cretaceous, Lower Cretaceous and Upper Oolitic (absent) Middle Oolitic Corallian Beds . . . Oxford Clay . . . Kellaways Rock & Clay Dull slate-coloured clay and shale . Grey shale and blue clay . . ? 10 f Lower Oolitic Great Oolite Series Cornbrash .... Forest Marble Series . Great Oolite Clay Great Oolite Limestone Upper Estuarine Beds White, ruddy, or blue limestone . Variegated clays and fissile limestones Blue and purple clay, with ironstone nodules White, or yellowish limestone . . Variegated clays, thin limestones, oyster beds, etc 15 8 12 25 30 Mesozoic, or Secondary Inferior Oolite Series Lincolnshire Oolite . Lower Estuarine Beds (part of North. Sand) Northampton Sand . Oolitic and shelly limestones & slates White and ruddy sands and clays, carbonaceous Ironstones, sandstones, calcareous beds 85 15 60 Liassic Upper Lias .... Middle Lias . . . Lower Lias . . . Blue clay, with cement stones and stone beds Grey micaceous clays, marls, cal- careous and sandy beds . . . Blue clays with cement stones and limestone bands 180 98 520 Triassic Rhaetic Beds . . . Keuper Bunter Black shale and white limestone, etc. Variously coloured sandstones and marls, etc (absent) 36 107 Permian (absent) Palaeozoic, or Primary Carboniferous Coal Measures . . . Millstone Grit . . . Carboniferous Lime- stone Series (absent ?) (absent ?) Dolomite, limestone, sandstone, marl, etc 190 Old Red Sandstone and Devonian Old Red Sandstone . Red sandstone, grits and marls to 105 Silurian and Cambrian (not yet found) Azoic Archaean Contemporaneous volcanic rocks . to 74
