On the Origin and Composition of Basalt. 153 



100 parts of the gelatinizing portion contains,- 



Silica, : . . . 



Alumina, 



Oxidulated Oxide of Iron, 



Oxide of Manganese, . 



lAme, 



Magnesia, 



Soda, . 



Potash, 



Water, 



35.13 



12.24 



15.30 



1.70 



8.08 



13.07 



3.05 



1.91 



4.59 



98.17 



Without doubt that part which does not gelatinise is completely 

 analogous in its composition to the basalt from Stetten. 



The gelatinous portion of basalt from Sternberg near Urach, 

 has likewise the greatest analogy in its composition with the pre- 

 ceding. In this basalt the portion that gelatinizes is very re- 

 markable : its proportion to that which does not gelatinize = 

 100.14. 



95.73 



Basalt from the vicinity of Wezlar. 



This basalt exhibits a very distinct decomposition on its sur- 

 face, consisting of two to four lines of bluish-grey, and where 

 the decomposition has proceeded farther, of a light yellow co- 

 lour. In tliis instance, the decomposed part, as well as that 

 which is undecomposed, requires examination. Of the former, 

 a part of that which was most completely decomposed was em- 

 ployed. The principal result was anticipated, as might be ex- 

 pected, namely, that the decomposition diminished the relative 

 proportion of the gelatinizing mass. 



