MINERALOGY. 



53 



microscope, as it appeared occupied with a sample of New Hampshire 

 infusorial earth.* The species represented are as follows : 



13. Fragilaria constricta. 



14. Gallionella distans. 



15. Gomphonema gracile. 



16. " truncatum. 



30. Lithodontium furcatiim. 



31. Spongolithis aspera. 



Soft parts of Plants. 



32. Pollen Pini. 



These organisms are excessively minute, and a cubic inch of this earth 

 contains many millions of individuals. 



Dr. A. M. Edwards has studied these earths, and in Vol. I of this geo- 

 logical report will be found a lengthy treatise on the diatomacese in 

 general, with illustrative plates. f The small figures here reproduced 

 are sufficient, however, to show those interested in the subject from a 

 mineralogical stand-point, the nature and composition of these interesting 

 deposits. 



This substance is also of considerable economic value. It is burned 

 till it is white, whereby the water and organic matters are removed, and 

 it then constitutes the best kind of polishing powder ; for, although they 

 are quite hard, the grains are so extremely minute that they scarcely 

 feel gritty between the teeth, and consequently the substance is emi- 

 nently adapted for polishing wares. This earth is soluble in caustic 



* Ehrenberg' s Mikrogeologie , T. xxxiii X. Also, Monatsbericht der Berliner Akaii. der Wissenschaften, 

 1845, p. 60. 



f Mr. H. L. Smith, of Geneva, N. Y., has also examined these earths, and is prepared to furnish a typical 

 series, embracing all the different species, properly mounted for microscopic study. 



