S 
22 Principles of Geology. 
planation which is suggested by consideration of one coast, will ap- 
ply, with almost equal accuracy, to all. Sea-cliffs, composed of 
solid rocks like mountain limestone or basalt, are liable only to that 
wearing of surface which is produced on the hardest stones by the 
impulse of water, and may remain, perhaps for ages, without any 
obvious reduction. Those composed of alternating strata suffer 
greater waste; for the softer parts are worn away by the unremit- 
ting attacks of the sea, and the harder ones being undermined and 
unsupported, fall in awful ruin. But where a cliff consists of gravel, 
sand, or clay, the destruction proceeds with alarming rapidity. ‘The 
Holderness coast is of this kind, and the records of its history shew 
the terrible devastations which it has endured. Almost within the 
memory of men now living, a church and church yard, having some 
land and buildings between them and the sea, have been swallowed 
up in the insatiable waves.* The substances which fall from the 
cliffs: angular stones of different sizes, gravel, sand, or clay. Ac- 
cording to their bulk and specific gravity, they are sorted and dis- 
posed of by the tide. 
Whoever has observed the sea-shore, with attention, is aware that 
the sand and pebbles, which constitute the beach, undergo continual 
change of place. The little heaps of gravel which are sometimes 
ranged in lines according to the height of the tide, are at other times 
strewed over the sand. According as the tide sets along the shore, 
the pebbles are driven onward progressively, accumulated in little 
quiet recesses of the cliffs, and heaped together in profusion in the 
larger bays. The large angular stones usually remain near the spot 
where they fell, but the smaller ones, after being rolled about by the 
waves till they become pebbles, are subject to the same progressive 
motion as the ordinary gravel; the sand travels in the same direction, 
and the finer particles of clay, mixed with and suspended in the 
water, are transported far away, and finally deposited on the marsh- 
es; and thus by the fall of the heights, materials are provided for the 
extension of the lower ground. ‘The wasted cliffs of Holderness 
have furnhised the pebbles which compose the long projecting point 
of Spurn, and part of the silt which enriches the marsh land along 
the rivers Ouse, Aire, Dun, and Trent. The sea engulphs but little 
of what falls from the ruin of its boundaries; its effect is to abate the 
high, and to raise and extend the low parts of its shores. When the 
-et adhue ostendere naute 
fe lent cum meenibus oppida mersis. OVID, METAM. XV. 
