Rev. J. Brodie on Level Terraces. 337 



waves is exerted in forming these level terraces. With this 

 purpose in view, let us trace the course of a pebble lying on 

 the beach. When the wave strikes against the shore, the 

 pebble is hurried upwards towards the land ; but when the 

 billow retreats, it is carried back. This process is repeated 

 again and again. If the retreating waves prove the stronger, 

 the stone is carried farther and farther back, till at last it 

 reaches a depth where the agitation of the surface can no 

 longer disturb its repose. Other pieces of stone or shell are 

 in like manner brought down and laid beside the first, and 

 others, again, are carried still farther into the deep, rolling 

 over the former ones, and resting behind them. In this 

 manner a terrace or level bed is formed beneath the water. 

 This deposition of sedimentary matter under the water is 

 not, however, the only level terrace that is produced by the 

 action of the waves. Every observer who has walked along 

 the shore must have remarked that, while many substances 

 swept backwards and forwards by the wave are gradually 

 carried into the deep, others are thrown up on the beach, 

 and there left dry. The material thus cast up, of whatever 

 kind it may be, does not find a resting-place till it has been 

 carried up beyond the reach of the highest flood. When the 

 land, to use a common expression, is gaining on the sea, and 

 the quantity of debris brought along by the tide is large, the 

 gravel, sea-weed, and shells thus drawn up form a terrace, 

 which varies in height according to the strength of the waves. 

 A similar agency produces level terraces on the sides of lakes, 

 and, on a smaller scale, on the sides of artificial ponds and 

 reservoirs. When the banks are steep and of friable mate- 

 rial, the billows raised by the wind wash down a portion of 

 the bank, and form a general deposit under the water, like 

 the lower terrace produced by the retreating waves of the 

 sea. On the other hand, when the banks slope gently down 

 to the water's edge, the floating mud, carried along by the 

 waves, settles down among the reeds and rushes that usually 

 grow in such situations, and, mingling with the decaying 

 vegetation, forms a level deposit which corresponds in some 

 measure to the terraces thrown up by the advancing billows 

 vol. m. 2 x 



