154 On tlie Origin and Composition of Basalt. 



The gelatinizing mass in proportion j The undecomposed Basalt, = 067,47*1 

 to that which did not gelatinize, I The decomposed Basalt, = 031,10.1 



100 parts of the gelatinizing mass of the undecomposed ba- 

 salt contains — 



Silica, 28.9 



Titanium, 6.63 



Alumina, 11.64 



Oxidulated Oxide of Iron, . . . 28.79 



Oxide of Manganese, . . . . 0.21 



Lime, 7-37 



Magnesia, 5.46 



Soda, 3.67 



Potash, 1.50 



Water, 5.32 



99.50 



The portion which did not gelatinize exhibited a peculiar 

 composition ; but the analysis must be repeated, as the loss is 

 so considerable : — 



Silica, 56.65 



Alumina, 9.16 



Oxide of Iron, . . . . . 3.99 



Lime, 12.65 



Magnesia, 3.91 



Soda, 3.17 



Potash, , 3.13 



92.66 



The quantity of alkali is remarkable, and it might be sup- 

 posed that it was acquired in consequence of the silica in the ge- 

 latinizing portion being separated from that which did not gela- 

 tinize by the carbonate of potash ; but that cannot be the case, 

 because the powder was first of all acted upon by diluted muria- 

 tic acid, and then carefully washed. 



The result of the investigation of the decomposed mass was, 

 that the quantity of silica, titanium, lime, magnesia, and the al- 

 kalis was diminished, while that of the oxide of iron was con- 

 siderably increased. 



Chrome has been found in all analyzed basalt ; without doubt 

 it is contained in olivine, and perhaps the chromate of iron is 



