176 



There may be others when they are furthcr looked over. 1 cletail 

 the method used in scarching the rocks for Bacillaria so that other 

 observers may see that care has been practiced in looking for these 

 atomies. Filtered water is always employed. The rock is broken up 

 and washed in filtered aqua ammonia. This is then nearly washed 

 off and bichromate of potash, finely pulverized, in excess is added, 

 and a small quantity of hydrochloric acid put in. The whole is wa- 

 shed in filtered water and aqua ammonia added. It is then dried 

 on a slide and a new solution of gum thus in wood spirit is added 

 and the cover put and pressed down. It is now examined, I do not 

 see how the Bacillaria can be introduced unless in the acids or the 

 wood spirit. But they are always the same and might introduce marine 

 forms but there are always fresh water forms in this case. The same 

 Solutions and acids were used to mount marine Bacillaria and they 

 bave not introduced fresh water forms there. Besides the shells were 

 often involved in the day. The following forms were found : 



Cymhella cisiula, II. 



Epithemia gìbha, C. G. F, 



— turgida, C. G. F. 

 Fragiìaria strìatula, L. 

 Melosira cremilata, F. T. K. 

 Navicula dicephala, C. G. E. 



— elliptica, F. T. K. 



— viridis, F. T. K. 

 Stauronds plwcnicenleron, C. G. E. 

 Synedra ulna, N. 



Sponge spicules of Spongia lacusiris, L. most likely 

 It must be remembered that silicic acid is always present in 

 the vegetables organisms and of the protista kingdom as colloid silica, 

 not crystaline at ali and soluble in fresh water and in saltwater 

 also. This is the reason why Bacillaria are so dijìcult to find when 

 present in specimens of rocks. They may be dissolved. Their shells 

 are sometimes made up of colloid silica, sometimes of aluminium 

 silicate (day) and sometimes of a compound containing carbon, com- 

 monly but wrongly called cellulose. In the latter case they dissolve 

 in water very readily. 



The meadow or meadows, for of cource we can not say which 



