( 414 ) 



néctioïi with the discussed decomposition of the rock. As follows 

 from the microscopic description, the considerable remainder of AI a O, 

 after saturation of rv,0, Na 8 and CaO in the feldsparmolecules must 

 at least for the greater part be attributed to the appearance of mus- 

 covite. If we take for muscovite the formula KH 2 Al,(Si0 4 ) s l ), the 

 A1 2 0, -remainder disappears' with the presence of 5.84° c orthoclase 

 bv the side of 9.15° muscovite. This last value, however, is exag- 

 geratedly high. If however, in accordance with a microscopic estimate, 

 a quantity of about 3% muscovite is assumed, and the remainder of 

 the Al s O, is equally divided over K,(), Na a O and CaG, iu the sup- 

 position that these oxydes in the same measure have been removed 

 by solutions, the following composition of the rock is obtained : 



quartz 28.32 Q = 28.32 ) 



orthoclase 12.79 , Sal = 95.60 



albite 40.87 F = 67.28 ' 



anorthite 13.62 ' 



muscovite 3.00 



hypersthene 0.89 j Fem = in 



magnetite 0.23 ) 



water 1.11 



Sum 100.83 



Now, if we leave muscovite, as of apparently secondary origin, 

 out of consideration, still then the rock takes the same place in the 

 chemical system : 



Sal 95.60^ 7 _ . 

 Fe^=ÏT2->ï' PerSalane 



Q 28.32 3 , _ 1 _ . M 



F = 67728 < 5 and > 7 • Bnttanare 



K^O + Na^ ■> 23 + 78 101 5 7 ^^ 



CaO 49 49 ^ 3 ^ 1 



K,0 23 3 1 



Na^O = 78<5 and > . , Lassenose. 



Against the name of lassenose can no doubt no serious objections 



be raised. 



Instead of hypersthene the rock contains amphibole and serpentine, 

 the first of which minerals being very rare, whilst the last mentioned is 



n Rosenbucch, Mikrosk. Physiogr. 1, 2. p. 262. J 905. 



*) To each of the K 2 0, Na,0 and CaO-molekules 5 has been added, of which 4 

 KoO molekules however, go to the muscovite, which is left out of consideration here. 



