The Aquarium 17 



material in the line of rocks is tufa or 

 tuff stone, a porous aqueous product. It may 

 be used both in its natural form as it is quar- 

 ried or in the shape of arches and grottoes, 

 constructed from small, well-selected pieces 



Fig. 8. Ornaments of cemented tufa. 



and bound together with cement. The 

 rough surface of the tufa favors the root- 

 ing of aquatic plants and some of the natural 

 cavities in the stone may be found large 

 enough for individual aquatics of small size. 

 It is most interesting to observe how the 



