GEOLOGY 
gives indications of shallow-water conditions, for its sandy nature and 
the presence in it of lignite, as at Oakley north of Bedford, point to the 
proximity of land, while its ammonites indicate that a fairly deep sea 
was not far distant. ‘The best sections are to be seen in the vicinity of 
Bedford, where it generally occurs as a calcareous sandstone with a thick 
bed of sand at its base and a thin layer of shelly limestone at its summit, 
from 7 to 10 feet of clay separating it from the underlying Cornbrash. 
The sandstone often takes the form of irregular concretions or ‘ doggers’ 
of varying size up to 10 feet in diameter imbedded in sand and some- 
times united in pairs like the figure 8. Many of these nodular concre- 
tions may be seen projecting from the sides of the cutting on the 
Midland Railway at Oakley. The clay contains selenite and ‘race’; the 
sand is destitute of fossils ; but the sandstone is very fossiliferous, having 
numerous Mollusca, including Myacites recurvus in abundance, and species 
of Ammonites, Ancyloceras, Pleuromya, etc. Gryphea bilobata and Belem- 
nites owent occur in shelly layers. 
Although the Oxrorp Cray is usually a greenish-grey and brown 
clay, it is by no means entirely clay. The following strata were pierced 
in a boring at Northill, three miles north-west of Biggleswade :— 
Boulder Clay, 104 feet. 
Oxford Clay : green clay, 12 ft. ; blue clay, 10 ft. ; blue clay and shells, 9 ft. ; dark 
green clay, 13 ft. 6in.; black stone, 4 ft. 6 in. ; greenish clay and shells, 20 ft. ; 
live sand, g ft.; sandy blue clay, 9 ft.; sand-rock, 7 ft. 4 in.; blue clay and 
shells, 2 ft. 6 in.; rock and blue clay, 1 ft. 9 in. ; limestone, 2 ft. 8 in. ; sandy 
blue clay, 3 ft.; blue stone, 3 ft. 6 in.; sandy clay, 4 ft. 10 in. ; limestone, 
4 ft. ; sandy clay and stone, 3 ft. Total depth, 223 ft. 7 in. 
This section is of interest not only for the great variation which it 
shows in the strata which here constitute the higher portion of the 
Oxford Clay, but also in bringing to light such an enormous thickness 
of boulder clay. In giving it Mr. H. B. Woodward” says that ‘ portions 
of the upper beds grouped with the Oxford Clay may represent the 
Ampthill Clay.’ Elsewhere there are bands of limestone near the top of 
the Oxford Clay, as at Sandy, 2 miles north-east of Northill, where 
there is stiff grey clay with ferruginous concretions, selenite, and a band 
of earthy limestone from 6 to 8 inches thick ; at Ampthill Park where 
the railway-cutting exposes dark blue clay with symmetrical crystals of 
selenite and seams of hard grey limestone varying from a foot to 18 
inches in thickness ; and at Ridgmont and Aspley Guise near Woburn. 
The great mass of the formation, which attains a thickness of nearly 
400 feet, is more homogeneous in character, indicating a prolonged 
period of deep-sea conditions over an extensive area, although near its 
base lignite and saurian bones have been found. It would appear that the 
sea-bed was sinking during its formation more rapidly than the sediment 
accumulated, and yet very slowly if the vast period of time which this 
accumulation must have occupied be considered. Its fossils are mostly 
pelagic forms, ammonites preponderating and Ammonites cordatus being 
1 Furassic Rocks of Britain, v. 51. 
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