28 THE UNIVERSE. 



cules, and as the schists of Bilin extend over a surface of 

 not less than eight to ten square leagues, and are from two 

 to fifteen feet thick, what an amount of vital activity there 

 must have been in this region to produce such a mass of 

 imperceptible skeletons ! 



12. Infusoria in Tripoli, from Richmond, Virginia, as seen with the microscope. 



Some tripolis of a red color are employed in house-paint- 

 ing ; others serve for cleaning our plate, dish-covers, etc. 

 A few years ago people little thought that the rose-color 

 with which we decorate our dwellings was due to the skel- 

 etons of invisible animalcules, and that it was they which, 

 from their silicious nature, enabled us to give a beautiful 

 polish to so many articles of copper. It is with the osseous 



