459 
either tlio Lure or Yare valley, and it may be that the accumu- 
lations in the valleys have something to do with the formation of 
the broads. In the Waveney the base may have been too porous to 
sustain such sheets of water; whereas in the Bure valley and in the 
iare valley they may bo supported by beds of laminated clay in the 
JNorwich Crag series (by some called “Chillcsford Clay”), of which 
we have examples at Wroxham, South Walsham, and Surlingham ; 
while the broads of Ormcsby, Martham, and Horsey are upheld by 
tue clays of the Lower Glacial Drift.* 
iho broads of Ormcsby and Frittou appear to bo alluvial valleys 
died with water, whoso egress is in great part prevented by artificial 
Chuns. Lroydon is probably tlie last remains of the estuarine 
chaiinel now all but choked up. Barton, and perhaps also 
Uickling, may have been formed by the cutting of turf, and they 
are, therefore, more or less artificial, f 
In other cases, as at ^Yroxham and Iloveton, the depression of 
10 land allowed the waters to overflow areas previously excavated 
m the widening of the valleys, and tidal influence aided for a time 
in scouring Biom out. The occurrence in the more remote broads of 
purely marine, or decidedly estuarine, species of Ostracoda and 
r ommini/eni, indicates the former presence of the sea. J 
Iho formation of the sand bank of Yarmouth, cutting off the sea 
c langed the character of the area; the waters, now entirely fresh’ 
could no longer hll the valleys, and they became dotted with 
broads. These are now gradually diminishing in expanse and depth 
accoiding to Mr. Gunn, at the rate of one foot in depth in twenty 
years. 
Tho subsidence before alluded to, perhaps, maiulj- helped to 
sepaiate Britain from the Coiitiiiont, aUoiviiig the sea to wear airav 
1.1 a comparatively short time, the chalky barrier that was left 
between our coast and France. 
AYe have referred to the many upheavals and depressions of the 
area, indicated plainly enough by the record of the rocks, and in 
# See Geological Survey Map, No. 67, by J. H. Blake. 
t* Geology of the Country around Norwirh ’ n ijq v 
Ihe Handbook to the Rivers and Broads,’ by G. C. Davies. ‘ 
: G. S. Brady and D. Robertson, Ann. Nat. Hist, series iv. vol. vi. p. 4 . 
1 I 2 
