35 



on which the to\\Ti of Greenwich stands. Perhaps the most im- 

 portant variation in the Tertiary beds hereabouts is the reduction of 

 the Blackheath pebble beds from a thickness of about 40ft. at 

 Bhickheath, to one of a few inches at Loampit Hill, Lewisham. 



The three influences that have affected the scenery of south- 

 eastern England (and elsewhere), apart from the nature of the rocks 

 themselves, are, firstlj'-, the movements of upheaval and depression 

 that have determined what kind of rock should present itself at 

 tlie surface at any given spot ; secondly, the action of the sea on 

 our coasts ; and thirdly, that of rain and rivers inland. North of 

 tlie Thames the cliffs are of soft clays, gravels, and sands, lying 

 directly or indirectly above the Chalk. They tend consequently 

 not only to recede rapidly, but to do so without producing those 

 gulfs and promontories that characterize coasts with well-marked 

 alternations of harder and softer strata. And as the shingle in the 

 east of England travels southward, in consequence of the superior 

 force of the flood-tide from the north as compared with that passing 

 up the English Channel, the mouths of the rivers Yare and Aide 

 have been deflected soiithward. The Broads of ]^orfolk are pools 

 in the course of the estuary, the waters of which, less than a 

 thousand years ago, covered the broad marshes now seen in the 

 lower parts of the valleys of the Bure, Yare, and Waveney. The 

 deposits of shingle and blown sand that have given a site for the 

 town of Yarmouth, and deflected the Yare southward, have been 

 the means of converting the former estuary into marshland. 



South of the Thames the outline of the coast is bolder, the 

 harder Chalk forming the promontories of the North and South 

 Foreland, and Beachy Head ; Culver Cliff and the Needles on the 

 east and west sides of the Isle of "Wight ; and Ballard Down, 

 north of Swanage Bay. At Dungeness Point and Pevensey Level, 

 we have estuaries silted up, and the alluvium more or less protected 

 from the action of the Avaves by the formation of shingle ridges on 

 the side of the alluvial tract next the sea. At Selsea Bill the 

 great destniction of the land by the waves has been to some degree 

 counterbalanced by the silting-up of an estuary that has converted 

 an island into a peninsula. The Isle of Wight OAves its existence 

 as an island to the destruction of the soft Tertiary strata of South 



