24, PRINCIPLES OF GEOLOGY. 



The natural agents now employed in altering the face of the globe, 

 are fire and water. The former forces fluid matter from the interior, and 

 spreads it around the volcanic mountains ; the latter is incessantly oc- 

 cupied in lowering heights, wasting and smoothing precipices, filling up 

 vallies, and equalizing the surface. 



ACTION OF THE SEA AND TIDE BITERS. The records of history 

 declare what large tracts of inhabited country have been lost in the 

 sea, and what extensive surfaces of new land have arisen to contract 

 the dominion of water. Observation shews on our own shores much of 

 the reciprocal process of demolition and augmentation ; and thus we 

 are enabled to form a correct estimate of the effects of this " war of 

 sea and land*." Every sea-coast, and especially every great estuary, 

 furnishes examples for contemplation ; and these effects are so similar 

 in all parts of the world, that the mode of explanation which is sug- 

 gested by consideration of one coast, will apply, with almost equal 

 accuracy, to all. Sea-cliffs, composed of solid rocks like mountain lime- 

 stone 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 com- 

 posed of alternating strata suffer greater waste ; for the softer parts are 

 worn away by the unremitting 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 f. The substances which 

 fall from the cliffs are angular stones of different sizes, gravel, sand, or 

 clay. According to their bulk and specific gravity, they are sorted and 

 disposed of by the tide. 



* Hutton. 



J- __ ^ et adhuc ostendere nautae 



Inclinata sclent cum moenibus oppida mersis. oviu, METAM. xr. 



