PLATE 9 



EXPLANATION OF FIGURES 



Views of specimen no. 6: a, upon dark, mixed sand (after one day); b, upon the 

 same sand, with the addition of white pebbles (after three days); c, on coarse, 

 reddish sand (after six days). 



Specimen no. f : showing conspicuously mottled appearance, unusual in a speci- 

 men just brought to the laboratory. 



496 



