i8o 



FORMATIONS AND GUILDS 



[Part II 



heaps it up into dunes (Fig. 97). The formations of the sandy sea- 

 shore and of dunes serve as excellent examples of the vegetation of 

 psammophytes, which are specially well developed in such spots. These 

 sandy strips of coast are usually subdivided into three zones— the foreshore, 

 between the ordinary high tide-mark and low tide-mark, the fiat mid-shore, 

 above the ordinary high tide-mark, and the dunes, which are heaped up 

 like hills between the shore and the mainland. 



Dunes are not always present. The sandy coast frequently rises quite 

 gradually, without any sharp separating line, into woodland or grassland, or the 



Fig. 95. Grand Canon of Colorado, Arizona. Stony river-bed. In the background are the deserts 

 that correspond to the climate. From a photograph. 



mainland rises abruptly beyond the flat shore, without assuming the character of 

 dunes. Such is the case either when the stretch of coast is relatively calm or 

 where the sand is either coarse-grained or largely mixed with pebbles and there- 

 fore heavier for transport by the wind. 



The following description of the vegetation on the sandy sea-shore of 

 Java can be taken generally as representative of the conditions of vegeta- 

 tion in such habitats: — 



The southern coast of Java is in parts covered with tracts of dunes 

 quite similar to those which, for instance, are so extensive along the 



