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 are 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 adhuc ostendere nautse 



Inclinata solent cum incenibus oppida mersis. ovid. metam. xv. 



