SEA BEACHES. 551 



of sea-sand by means of land-springs.^ The shell-sand at Bude has been largely 

 used for agricultural purposes ; while sand from the Warren at Exmouth has been 

 employed for moulding. At Babbacombe Bay portions of the shingle beach are 

 cemented into a conglomerate by calcareous springs ; and near Llandrillo Bay 

 there is a mass of similar conglomerate with recent marine shells. - 



Springs charged with much iron-ore that issue from cliffs by the sea frequently 

 cement the shingle and sand into a hard stone : instances occur near Bolt Head, 

 as observed by the Rev. J. Pulliblank. The decomposition of old pistols and 

 nails has frequently given rise to masses of ferruginous conglomerate, that may be 

 picked up on the beach, as near Cromer.-' 



The influence of Sea-water in producing a slight amount of alteration in 

 rocks that have been long exposed to its influence is a subject deserving attention. 

 Mr. J. A. Phillips observes " that while the slates of Botallack are highly 

 magnesian, the sea-water which percolates through them into the workings of the 

 mine has lost three-fourths of its magnesium. Similar effects appear to have been 

 produced at Huel Seton, where the amount of magnesia in the rock bounding the 

 great cross course, which is traversed by the modified sea-water constituting the 

 well-known "lithia-spring," is twice as large as it is in the normal killas of the 

 locality.^ 



The induration of rocks on the sea-coast has been noticed in Glamorganshire 

 (see p. 266) ; in Yorkshire (Lower Estuarine Series) j^ and at Hunstanton.^ 



Sea Beaches. 



The pebbles of a sea-beach may be shaped directly from the 

 rocks which form the cliffs, they may be derived from old beds 

 of conglomerate, or from more recent beds of gravel or shingle or 

 stony clay that constitute the whole or a portion of the cliffs. 

 Again, they may be derived in any one of these ways, and have 

 travelled a considerable distance from their source. The majority 

 of the stones on our beaches, whether pebbles or subangular frag- 

 ments, are formed of Chalk-flint, quartz, quartzite, and various 

 kinds of sandstone ; stones of a more or less siliceous nature, 

 standing the wear and tear of course much better than limestones. 

 Locally we find limestones and fragments of other rocks derived 

 from adjacent cliffs ; even clay-pebbles or clay-balls are not un- 

 frequent on coasts where the cliffs are formed of clay. Sometimes 

 these clay-balls when rolled about attach to themselves numbers 

 of small pebbles, and appear like masses of pudding-stone. Such 

 clay-pebbles may be seen near Cromer, Lyme Regis, etc. 



Many stray pebbles whose origin might otherwise be difficult to account for, may 

 be brought as ballast, or be due to the shipwreck of vessels carrying stone, 

 or to the unlading of stone to be used for various purposes. Thus Plymouth Lime- 

 stone is brought to Bridport Harbour for road-metal, and fragments of it are 

 sometimes found on the beach. 



On many parts of the coast agates, carnelians, and other pebbles capable of 

 being polished for ornamental purposes are collected. At Aberystwyth agates and 



^ Journ. Chem. Soc. (2), i. 30. 

 - Miss Eyton, G. Mag. 1868, p. 352.. 



^ S. Woodward, Mag. Nat. Hist. ix. 47; see also W. S. Gresley, G.Mag. 

 1886, p. II. 



* Q. J. xxxi. 324. 



5 C. F. Strangways, Explan. Sheets 95 S.W. and S.E. (Geol. Surv.), p. 3. 



6 Rose, Phil. Mag. (2), vii. 185. 



