462 
Geology of Norfolk. 
neath the sand-hills and the alluvium of the Yare. Detachrd 
portions of the clay are, however, met with in the " hards " or 
" holms " which rise like islands from among the alluvial depo- 
sits. In composition this clay is somewhat different from that of 
the Cromer cliffs, consisting of a mixture of blue clay, such as it 
occurs in these cliffs, with yellow clay and sand. In this form it 
is the grey clay-marl of East Flegg described by Marshall. 
South of the Yarmouth estuary it is again visible in the cliffs 
between Gorlston and Lowestoffe, occupying their upper part, 
with a large development of crag- sand below it, and a thin cover- 
ing of the sands and gravels of the upper drift above it. 
Following it up the valley of the ^^ aveney, we find it still 
holding the same relative position to these two sandy deposits, 
except where, by the denudation of the upper sand, the clay has 
been exposed over extensive areas in the southern hundreds of 
Norfolk, and over a still more extensive portion of the north of 
Suffolk. Oolitic detritus increases in quantity as the till is traced 
towards the west, in the river sections, and in the clay-pits which 
have been so abundantly opened throughout the district. This 
detritus consists of fragments of the Kimmeridge clay and other 
oolitic rocks, with their characteristic 'fossils ; among which, 
vertebrae of saurians and the septaria of the Oxford clay, known 
by the name of turtle-stones, abound. Mr. Rose of Swaffham 
possesses an extensive collection of these bouldered fossils, and 
Woodward's ' Geology of Norfolk' contains a catalogue of them, 
with the strata from which they have been derived. The ooliiic 
sandstones frequently occur as large unabraded blocks. The 
Kimmeridge clay is seen sometimes under the form of accumu- 
lated masses of its unmixed fragments, sometimes in small pieces 
dispersed, with fragmentary chalk, through yellow clay mixed 
with sand. 
In the northern parts of central Norfolk, and in the ramifica- 
tions of the till among the chalk, the chalk detritus increases in 
Cjuantity till it constitutes the largest portion of the mass, whicli 
then is scarcely distinguishable from the transported and recon- 
structed chalk to be mentioned presently, as enveloped in the 
"upper drift of East Norfolk as well as in the till. This form of 
till abounds in the neighbourhood of Wells, constituting the 
" clay" which has been so extensivelv and profitably used on the 
Holkham estates. The least chalky varieties have been found 
the best. In the drift of the Cromer cliffs the chalk detritus has 
been chiefly derived from the soft upper beds; in that of south- 
ern and central Norfolk, fragments of the lower or hard chalk 
prevail. The masses of transported Kimmeridge clay aiul chalk, 
associated with irregular accumulations of sand and gravel, which 
occur in hollows on the summit of the watershed, may be coiisi- 
