GEOLOGY OF THE NORWICH DISTRICT 51 
Echinocorys scutatus Leske can be collected, as well as an interesting 
assemblage of gasteropods. Other fossils, typical of the main mass of 
the zone, which can be found in chalk-pits on the southern and 
western limits of Norwich and at Coltishall, include Belemnitella 
mucronata (Schlotheim), Ostrea vesicularis Lamarck, Rhynchonella limbata 
(Schlotheim) var. lentiformis S. Woodward, R. plicatilis (J. Sowerby), 
Carneithyris carnea (J. Sowerby), Terebratulina striata Wahlenberg, 
Chatwinothyris symphitica Sahni, Crania costata G. B. Sowerby, 
Typocidaris subvesiculosa (d’Orbigny), and Bostrychoceras polyplocum 
(Roemer). 
Scattered about the district, and also on the shore west of Cromer, are 
the curiously shaped ‘ paramoudras,’ which consist of masses of flint 
of roughly cylindrical form, often a foot or two in diameter and up to 
4 ft. in height, with a hollow centre. The tubular cavity is vertical 
as they lie in the Chalk. Their mode of origin is not fully understood, 
but it is probably concretionary, although Lyell compared their shape with 
that of giant sponges. Variations in shape, however, pass through all 
gradations down to the well-known irregular nodules. 
The Chalk of Trimingham, on the Norfolk coast, has now almost 
disappeared as a result of marine erosion. It belongs to a still higher 
division of the Chalk, namely, the zone of Ostrea lunata, and constitutes 
the only occurrence of this zone in England. The Chalk occurs in bluffs 
in the cliffs and on the foreshore, and is often yellow-stained and dis- 
turbed, presumably by glacial action. Much controversy has raged over 
the question as to whether these chalk-masses are transported blocks or 
are in situ. If transported, they are likely to have come from an outcrop 
close at hand, for they occur at just about the position which might be 
expected in relation to the outcrops of the other zones in Norfolk. The 
thickness of the Junata-Chalk is estimated at about 70 to 80 ft. Flints 
are abundant and often of curious form. Fossils occur in bands of the 
Chalk, and include Ostrea lunata Nilsson, O. vesicularis Lamarck (true 
form), Terebratulina gracilis Schlotheim and T. gisei Hagenow, Belemni- 
tella mucronata (Schlotheim), Echinocorys scutatus Leske, Chatwinothyris 
subcardinalis Sahni, bryozoa, etc. 
III. Tertiary. 
After the great period of steady marine transgression which accompanied 
the deposition of the Chalk, a general upheaval brought the British area 
above sea-level, and a process of planing down ensued. The Chalk was 
tilted until its general dip was eastwards, and the south-east of England 
- was once more submerged beneath the waters of the Eocene sea of the 
Anglo-Belgian basin. This sea encroached only on eastern Norfolk, and 
some of the deposits then formed, the Reading Beds and London Clay, 
were preserved, as has been demonstrated by deep boreholes like that at 
Yarmouth. But the Chalk of our area, being at the north-eastern limit 
of the London Basin of deposition, remained for the greater part bare 
until, in Pliocene times, the ancestor of the North Sea came into being. 
From those times to the present day, the geological story is one of gradual 
