516 



SILTING UP OF ESTUARIES. 



[Ch. XX. 



ment commenced .* But the example just given will satisfy 

 every geologist that we cannot ascertain the starting-point 

 of dunes, all coasts being liable to waste, and the shores of 

 the Low Countries in particular, being not only exposed to 



times 



some 



be made 



minimum 



must be 



of level. The dunes may indeed, in 



use of as chronometers, to enable us to assi 



of antiquity to existing coast-lines ; but this 



applied with great caution, so variable is the rate at which 



the sands may advance into the interior. 



Hills of blown sand, between Eccles and Winterton, have 

 barred up and excluded the tide for many hundred years 

 from the mouths of several small estuaries ; but there are 



om 



made through these, by which immense damage 



done to the low grounds in the interior, 

 of Happisburgh, also, are hills of " " 

 Yarmouth. These dunes afford a 



miles 



temp 



s 



Winterton 



must 



formerly farther than at present. 



Silting up of 



At Yarmouth, the sea has not 



advanced upon the sands in the slightest degree since the 

 reign of Elizabeth. In the time of the Saxons, a great estuary 

 extended as far as Norwich, which city is represented, even 

 in the thirteenth and fourteenth centuries, as < situated on 

 the banks of an arm of the sea.' The sands whereon Yar- 



became firm 



t> 



the year 1008, from which time a line of dunes has gradually 

 increased in height and breadth, stretching across the whole 

 entrance of the ancient estuary, and obstructing the ingress 

 of the tides so completely, that they are only admitted by the 

 narrow passage which the river keeps open, and which has 

 gradually shifted several miles to the south. The ordinary 

 tides at the river's mouth rise, at present, only to the height 

 of three or four feet, the spring tides to about eight or nine. 



* De Beaumont, (u'ologic Pratique, p. 218. 





