i8 THE BOOK OF NATURE STUDY 



On sandy seashores the following belts may be observed : 



1. The foreshore. This is the strip between the ordinary 

 high-tide mark and low-tide mark. This is periodically washed 

 by the waves, and presents alternately terrestrial and aquatic 

 conditions. It is almost constantly exposed to the spray ; 

 evaporation goes on rapidly, and the temperature is constantly 

 changing. The vegetation is in consequence limited, consisting 

 mostly of annuals or perennials with long creeping rhizomes. 



2. The midshore comprises the belt of sand between ordinary 

 high tide and spring tides. 



3. The upper shore is the strip between the middle beach 

 and the sand-dunes, if these are formed. There is more humus 

 in the soil, because there is more vegetation. The spray of the 

 waves reaches this belt, and sand is constantly being blown by 

 on-shore winds from the midshore. 



4. If sand-dunes are formed they will occur to landward of 

 the upper beach, but dunes are not always present. The sandy 

 coast may rise quite gradually without any sharp line of separa- 

 tion into woodland or grassland. The formation of dunes depends 

 very largely on the direction of the prevalent wind. 



The influence of the wind is also very evident in the distance 

 to which the spray of the waves may be carried, making the 

 atmosphere salt ; this is very well seen off the Cornish coast, where 

 the storms are often very violent. The branches of the trees 

 grow with an inclination towards the opposite direction from that 

 whence the wind blows, so that the trees seem one-sided. 



5. On pebble beaches the following observations are suggested. 

 The larger stones are heaped up on the higher part of the 



beach, forming a ridge, the smallest pebbles being nearest the 

 sea. 



The shape of the pebbles is flat, not round, as in rivers. This 

 indicates that they have been pushed, not rolled along. 



The shingle is very generally arranged in festoons or scallops, 

 sometimes for miles in length. This arrangement has been attri- 

 buted to the crossing of waves. 



The effect of a strong on-shore wind, or of a heavy ground 

 swell on the shingle, should be noted. It may be almost entirely 

 carried away. 



