26 REVIEWS. 



shell of flint, which almost always presents upon its surface the most 

 exquisite sculpture, varying from species to species, and in its delicacy and 

 beauty exhausting our conceptions of decorative form. 



These wonderful little bodies are sometimes solitary ; but they are often 

 found associated into companies, in which the individual members are 

 united to one another, so as to form curious zig-zag chains, or flat ribbons, 

 or radiating fans, or elegant little trees. When exposed to the action of 

 strong acid or of fire, the soft, vegetable cell is consumed, and the flinty 

 case remains behind entirely unaltered, and retaining all its beautiful 

 sculpture ; and though thousands of years may have passed away since 

 the living vegetable was encased within its walls of flint, this same 

 sculpture will be preserved as perfect as if it were only a thing of 

 yesterday. 



To become the possessor of the extraordinary productions we have thus 

 attempted to describe, you have only to make a careful search in the 

 nearest stagnant pool, or running brook, or along the sea-shore at low 

 tides ; you will be then almost sure to find multitudes of Diatomacece- 

 for such is the name given by naturalists to the bodies now under consi- 

 deration forming a brownish-yellow covering, like fine down or velvet, 

 on the stems and leaves of various water plants, or on submerged stones, 

 er spreading over the mud at the bottom of the water, or floating as a 

 a thin film upon the surface. The Diatomaceae being thus recognised, you 

 are to collect them from the different localities, in small, wide-mouthed 

 phials. It is, in most cases, impossible to obtain them at the time of col- 

 lection free from mud and other extraneous matter ; but, to separate them 

 from the various impurities with which they are associated, you have only 

 to expose them in water for a few hours to the light of the sun, admitted 

 through the window of your room, and then, by that mysterious sympathy 

 which exists between light and organized beings, the Diatoms will separate 

 from the surrounding impurities, and congregate at the light side of the 

 vessel. 



But when once the Diatoms are in your possession, and you have fitted 

 them, by separation from extraneous matter, for examination under the 

 microscope, an important question at once suggests itself How are you 

 to proceed in the study of them ? how are you to find out all that is 

 already known about the produce of your day's collection ? and how are 

 you to satisfy yourself that any particular species has been already described, 

 or may not be a totally new form which you have been so fortunate as to 

 discover ? 



Two years ago this would have been a difficult task for the English natu- 



