I/O PHYSIOGRAPHY. [chap 



has pointed out that the Isle of Sheppey has suffered con- 

 siderably by the inroads of the sea, fifty acres of land 

 having been lost within the short space of twenty years, 

 though the cHffs there are from sixty to eighty feet in height. 

 Heme Bay, on the Kentish coast, has lost land to such an 

 extent that it no longer retains its shape as a bay. Going 

 yet further out into the estuary of the Thames, we find a 

 notable illustration of marine destruction at Reculver. 

 This was the old Roman station of Regiilbiujn. Not only 

 has the sea entirely destroyed the military wall, but the 

 church, which in the time of Henry VIH. was nearly a mile 

 inland, is now on the very brink of the cliff; and, indeed, it 

 has only been saved from actual destruction by artificial 

 means. As the two towers of the church form a well-known 

 landmark to mariners, a causeway has been constructed on 

 the beach to arrest the progress of the sea. 



If the sea were a body of water in perfect repose, it 

 would be utterly incapable of effecting mechanical erosion. 

 But every one knows that the sea is never absolutely at rest, 

 and that, even in the calmest weather, its surface is ordi- 

 narily more or less troubled with waves. It is easy to 

 understand how these are formed. When you blow upon 

 the surface of a basin of water, the mechanical disturb- 

 ance of the air is immediately imparted to the liquid, 

 and the surface is thrown into a succession of ripples. 

 In like manner, every disturbance of the atmosphere finds 

 its reflex on the surface of the natural waters. Each puff 

 of wind catches hold of the water, and heaps it up into 

 a little hill with the face to leeward ; then the crest falls, 

 and the water sinks down into a trough, as deep below 

 the mean surface as the hill was high above it ; but the 

 next column of water is then forced up, only however to 

 be pulled down again, and in this v/ay the motion of the 



