of extensive Conglomerate and Gravel Deposits. 1 6S 



lent examples are seen on our southern coast, where the pre- 

 valent winds being W. or S.W. the beaches travel eastwards. 

 If rocky projections or points of land occur on the east of any 

 shingle beach so travelling, the sea soon forms a considerable 

 barrier against itself, more particularly when the mouths of 

 valleys or flat lands back the shingles ; such flat lands or 

 mouths of valleys thus obtaining protection from the ravages 

 of the sea (Plate II. fig. 2). If the streams which discharge 

 themselves into the sea from such valleys or flat lands are small, 

 their mouths ai'e barred by the beach, and the water perco- 

 lates through the shingles. Such streams, in cases of flood, cut 

 through the shingle a passage again to be dammed up by the 

 effects of a gale of wind. 



It would appear that though shingle or pebble beaches 

 travel coastways, in consequence of the general direction of 

 the breakers, there is no evidence of their being transported 

 outwards or into the depths of the ocean. The seaward front 

 of most shingle beaches, particularly when they defend tracts 

 of flat country, is bounded by a line along the edge of the 

 beach ; above this line the beach generally makes a consider- 

 able angle with the sands, in cases of sandy flats. 



In cases where shingle beaches are not entirely quitted by 

 the tide, sandy, shelly, or very fine gravel soundings are 

 commonly obtained a short distance from the shove, unless the 

 bottom be rocky, in which latter case it is generally a mixture 

 of sand, rock, or fine gravel* and shells. In fact, if the present 

 continents or islands were elevated above, or the sea depressed 

 beneath, the present ocean level, shingle beaches would be 

 found to fringe the land, but not to extend far seaward. 



It is but rarely that the pebbles on shingle beaches are found 

 to have travelled considerable distances, even along shore ; in 

 the Chesil Bank indeed, — that extraordinary ridge of pebbles 

 about sixteen miles long, which connects the Isle of Portland 

 with the main land, — the shingles seem to have travelled twenty 

 or thirty miles from the westward. This bank is remarkable 

 on many accounts, and among others for the power the sea 

 has exhibited of heaping up a barrier against itself, even when 

 not backed by land, provided it has two solid resting places 



* 'J'liesc gravels arc generally fine, very different in size from the com- 

 mon shingles of beaches. It might be supposed by persons unaccustomed 

 to take soundings, that the gravels marked on charts were coarse, resem- 

 bling shingles; but in general such gravels do not exceed the size of a nut, 

 and are mojt connnonly smaller. Such fine gravels are very frequently 

 mixed with shells; and no soundings are more common on coasts, particu- 

 larly our own coasts, than gravel with shells, sand and gravel, and sand and 

 shells. 



Y 2 for 



