282 THE CRETACEOUS ROCKS OF BRITAIN. 
cutting, the recognisable ingredients being small shell-fragments, 
a few “ spheres ” and Foraminifera, and much fine sand and argil¬ 
laceous matter, the sand grains being smaller than at Charlton. 
As at Charlton, the marl passes rapidly up to a more calcareous 
deposit with fewer but larger shell-fragments and a greater abund¬ 
ance of “ spheres.” 
Glauconite occurs in all specimens, but the grains are small and 
widely separate. Sponge-spicules are not infrequently seen, but 
are nowhere abundant. 
Passing into Cambridgeshire we find at Barrington 10 feet 
above the Cambridge Greensand a deposit very similar to that 
at Arise} 7 . Specimens from higher horizons show that as we pass 
upwards the marl loses its sandy and siliceous character, 
mineral grains become smaller and rarer, “ spheres ” more numerous 
anl shell-fragments more irregular in size. Nearer Cambridge the 
same phases occur. 
Norfolk and Suffolk .—In North-west Suffolk and in the south¬ 
east corner of Norfolk (Stoke Ferry, Shouldham, &c.), the amount 
of fine siliceous inorganic material is hardly appreciable to the eye, 
anl sand grains are rare. In the majority of examples from the 
lower two-thirds of this zone fine amorphous calcareous material 
constitutes 75 per cent, of the deposit; “ spheres,” shell-fragments of 
irregular size, neither in exceptional abundance, a few Foraminifera 
and minute sand grains form the remainder. In the upper part 
of the zone shell-fragments and spheres are more numerous. ^^ 
In North-west Norfolk (Dersingham, Snettisham, Heacham) the 
structure of the marl becomes more irregular in its upper part. 
“ Spheres ” are common though not abundant, and many prisms 
of Inoceramus shells occur in all examples. Globigerinxe and a few 
other Foraminifera occur, but they still form a very small part of the 
deposit. In several slides there are fragments of Hexactinellid 
sponge-mesh, the silica of the spicular walls being replaced by 
calcite. 
The lateral passage from a marl to a chalk culminates at Hun¬ 
stanton. Here the successive portions of the zone exhibit well- 
marked differences of structure, viz., the “ Sponge Bed,” the “ Inoce- 
ramus Bed,” and the white hard beds which lie between this last 
named anl the Totternhoe Stone. 
Of the Sponge Bed (20) rather more than half consists of fine 
amorphous material, once probably a hue calcareous mud, but now 
in a coniition of finely granular crystalline calcite. “Spheres” 
are abundant at the base of the bed, less so towards the to}). Fora¬ 
minifera, though not numerous, are well shown in outline, and 
amongst them the form of a Globigerina is prominent. These with 
the cells and “spheres” form about 30 per cent, of the deposit. 
Shell-fragments scattered through the mass form perhaps 10 per 
