10 THE AQUARIAN NATURALIST. 



and well-being of its intended inhabitants. Here 

 (and the arrangement is of considerable importance) 

 we must study Nature. The floor should be composed 

 of smooth washed shingle, the stones resembling in 

 size a pea, a bean, up to a hazel-nut, as a substratum ; 

 but with, here and there, a larger piece, whose bulk, 

 like Skiddaw or Helvellyn, so to compare great things 

 with small, may protrude through the alluvial plain to 

 be deposited above. Upon the top of this, a stratum 

 of fine sand (sea-sand) should be spread to the depth 

 of at least three-quarters of an inch or more. 



The uses of this sea-sand are, in some measure, as 

 we shall find hereafter, important in relation to many 

 species of marine animals that hide themselves under 

 its shelter, or derive from it the materials wherewith 

 to build their habitations; but at present we must 

 regard it in its Hygeian character, in so far as it is 

 important to the maintenance of the health of the 

 entire community. 



Whoever upon the sea-shore takes the trouble 

 to dig to the depth of a few inches, more or less, 

 according to the peculiar circumstances of the locality, 

 will find beneath the clean and wholesome sand a 

 layer of black, or bluish, paint-like, stinking slime, 

 the dregs and filth deposited, as it were, by filtration. 

 Any one who has stood upon the beach where the 

 receding tide, by washing away the surface-sand, 

 and laying bare this foul accumulation, has thus 

 stirred up the abominable odours of the Stygian 

 pool, can vouch for the deleterious effluvia that ema- 

 nate from this pestiferous deposit, which, were it not 

 thus safely buried, would poison the entire coast, and 



