NATURE'S JEWELS. 173 



and their almost indestructible coverings fall to the 

 bottom of the water, forming in many cases vast 

 deposits on the floor of the ocean, the mouths of 

 rivers, and the beds of fresh water lakes, &c. Or 

 the living Diatoms are devoured by fishes, and 

 these in their turn by birds ; and though thus sub- 

 ject to a double digestive process, their silicious 

 valves turn up again in guano, and when cleaned 

 and mounted are objects of great beauty. Indeed 

 it is the casket, and not the priceless life gem it 

 contains, which has attracted most attention to the 

 Diatom ; and this is not to be wondered at, or even 

 deplored, when its varied and beautiful form and 

 exquisite sculpturing are considered. 



Variety is a general law in all kinds of life, but 

 in many of its lowly forms (as we have seen) this 

 is characterised by great irregularity. The reverse 

 is the case in the Diatomacea, where symmetry 

 is the universal law the valves and the engrav- 

 ings on them being formed with mathematical 

 accuracy, and matchless artistic delicacy and skill. 

 Any attempt, however, at verbal description not 

 only cannot do justice to this part of our sub- 

 ject, but would rather damage it than otherwise. 



