768 DESCRIPTIVE GEOLOGY. 



ate. If gently heated, the rock assumes a slight grayish tinge, passing off 

 at a higher temperature, which would suggest the presence of a small 

 amount of organic matter. 



Mr. R. W. Woodward subjected the infusorial silica to chemical anal- 

 ysis and obtained as a result : 



Silica 86.70 86.91 



Alumina 4.09 4.00 



Ferrous oxide 1.26 1.22 



Lime 0.14 0.11 



Magnesia 0.5 1 0.51 



Soda 0.77 0.80 



Potassa , 0.41 0.36 



Phosphoric acid trace trace 



Water 5.99 5.89 



99.87 99.80 



Under the microscope, even with a moderate power, these siliceous 

 beds are seen to be made up of innumerable fragments of Biatomacea. Dr. 

 C. G. Ehrenberg,^ of Berlin, Prussia, to whom were sent a large number of 

 specimens from this locality, has described no less than 33 distinct organic 

 forms, one of which may belong to the vegetable world. Of these forms, 

 12 have been classed as Polygastera and 20 as Fhytolitharia, the most abundant 

 species being: 



Oallionella granulata. 

 Gallionella sculpta. 

 Spongolithis acicularis. 



Accompanying Dr. Ehrenberg's work is a plate giving the microscop- 

 ical sections of the infusorial earth from this locality, together with others 

 from the Truckee Valley and Salt Lake Desert. 



The palagonitic tufas show considerable differences in superficial ap- 



* tjber (lie wachsende Keiintuiss des uasichtbareu Lebeus als feldsbildende Bacil* 

 larien in Californieu, Berlin, 1870, IS. 



