EXCURSION TO WALTON AND fRlNTON. ^ig 



be partly due to inaccuracy in the survey of 1838, or the opera- 

 tions for protection of the coast, although somewhat inadequate, 

 may have retarded the waste, as far as is perceptible on the 

 small-scale map, one inch to the mile. The difference indeed 

 are chiefly in the opposite direction, that of increase of the land. 

 Considerable areas are shown in the new map as enclosed from 

 tidal access in the interesting area of Hamford or Hanford 

 Water, west and northwest of the Naze. Some of these have 

 since been regained by the sea, either through accident or 

 neglect. But outside, and apart from human action, deposition 

 has been proceeding, and the new map shows a projecting spit 

 of sand (the Pye Sand), nearly a mile in length beyond the low- 

 water line of 1838. This, coupled with the fact, informally 

 mentioned by Mr. Mothersole at the excursion meeting, of the 

 presence of quantities of Crag shells on the beach in that 

 direction, far beyond the outcrop on the Naze, points to a 

 northerly shore-current thereabouts, as a backward eddy from 

 the general southward tendency, so fully evidenced at the groins 

 and breakwaters along the Naze and towards Frinton. These 

 are banked up to the top with sand on the north side, whilst to 

 the south of each the bare London-clay forms a black slippery 

 surface, full of water-holes. 



Seawater, apart from its motive force, tends to preserve the 

 London-clay, by excluding atmospheric air, and maintaining a 

 state of saturation. It is the alternation of drought and wet 

 that breaks up the fairly-solid clay, converting its abundant iron- 

 pyrites into oxide of iron and free sulphuric acid, the latter in 

 its turn attacking the carbonate of lime generally present. Both 

 the ferric oxide and tlie sulphate of lime occupy greater bulk 

 than m their previous combinations, apart from that of the 

 carbonic acid gas set free by the later re-action. Some change 

 possibly takes place also in the elements of the clay itself, for it 

 passes from a rather tough mass, but one which will break into 

 fragments, to a plastic dough, which can only be torn or 

 squeezed apart. Perhaps in the absence of sufficient carbonate 

 of lime, the sulphuric acid attacks the alumina of the clay, or 

 the change may be purely molecular. At any rate, the modifi- 

 cation proceeds inwards from every crevice, and each expansion 

 produces further Assuring, until the mass, even at an early stage 

 of the process, is traversed in every direction by cracks with 

 slimy surfaces. A little excess of rain, and these surfaces are 



