Chap. I] 



THE FORMATIONS 



179 



where mutual attrition reduces them, partly to pebbles, partly to sand, 

 and where the weathered felspars are ground into finely grained earthy 

 clay. A change in the water-level leads to deposits in river-beds and 

 along their banks of masses of pebble, sand, and clay, which are some- 

 times more, sometimes less, frequently, or only exceptionally, covered 

 again by the water. Such deposits bear an open vegetation, which is 

 in some cases more transitory, in others more lasting, and the species 

 growing on them are for the most part characteristic of such habitats 

 (Figs. 94-9 6 )- 



Fig. 94. Stony tracts in the bed of Craigieburn river, near its opening into Lake Pearson, in the 

 forest region of the Southern Island of New Zealand, 600 meters above the sea. Ozothamus depressus, 

 Hook, f., and Epilobium melanocaulon, Hook. f. From a photograph by Cockayne. 



The fragments of the rock finally reach the sea along the water-courses. 

 If the sea-shores are flat, sand, clay, and small pebbles are thrown up 

 by the action of stormy waves on the land to distances more or less 

 above the usual high tide-mark, and their deposits, if neither too much 

 turned over by the wind nor carried back into the sea, within a few 

 months bear some vegetation. If this can maintain itself, these new 

 deposits become gradually fixed and definitely united to the land. 



Of the sea-shore deposits, sand is the most extensively developed, as 

 the wind carries it further inland than clay and pebbles, and frequently 



N 2 



