451 
being ultimately cleared out, the clayey strata are exposed. In 
one case I noticed a narrow gorge, nine feet deep and two and a 
lialf to throe feet wide — like a miniature canon — at the bottom of 
one of these chines. Many riv'ers commence in a subterranean 
course, to which numerous streamlets contribute j and the sources 
of our present rivers may be at different levels according to tlie 
amount of rainfall which saturates the porous strata and swells 
the numerous feeders at its source. Such is the case with the 
Wensuin in its gravelly valley near Syderstone, and (as pointed 
out to me by Mr. Whitaker) with the Babingley liiver near 
^lassingham. In these cases the fluctuations arc caused by the 
level of saturation in the Chalk. And streams flowing for a time 
underground, and carrying away material from below, will cause 
the surface to sink. The low-lying gravelly tract at Fulmodeston 
Gorse seems to have been produced in this w'a}’. 
Fronr these and other considerations, we may be able to under- 
stand how some of our great sheets of gravel and sand, like those 
of the neighbourhood of Holt and Cromer, have become isolated 
lulls -with numerous ramifying spurs ; for although some of the 
great sheets of gravel znay have been deposited in patches, yet the 
surrounding strata have been denuded, and they themselves have 
perhaps been broken up into smaller patches or outliers. And 
\^hen once this has taken place, the surface features of these sandy 
and gravelly tracts may remain for long periods much the same, 
although the level of the whole may be slowly reduced by springs 
carrying away material from the lower portions of the strata at 
their junction with clayey beds beneath. 
These remarks may apply to the numerous little sandy hills to 
bo seen dotted about from Cromer Avestwards along the coast by 
Sherringham to Weybourn, and again at Glandford, Bayfield, and 
Blakeney. In this district wo find a long and tortuous ridge of 
gravel and sand formizig the Blakeney Downs, looking in places 
like a great railway eznbankment, and small gravel hills, little 
larger than tumuli, sometimes covered avith Gorse and Broom in 
the midst of ploughed fields, at other times looking like artificial 
heaps, there being little or no earthy matter in the densely-packed 
mass of stones. Perhaps the earthy matter has been washed away 
by lain, but their porous nature has, no doubt, helped to preserve 
them, just as an}’’ earthworks of early I'accs are more likely to be 
