330 RECOKI) OF SCIENCE FOR 1887 AND 1888. 



California, it is shown that the presence or absence of free quartz is uot 

 necessarily dependent upon the chemical composition of the magma, but 

 that forms in which the mineral is abundant mn,j yield on bulk analysis 

 as low percentages of silica as those in which it is quite lacking. It is 

 also shown that a rock from the Yellowstone Park having a composition 

 almost identical with that of Diller's quartz basalt has the mineralogical 

 composition and structural features of a quartzose diorite. Mr. Iddings's 

 conclusions are that these quartzes are primary crystnllizations from 

 the molten basaltic magma and exhibit no definite relations to its chem- 

 ical composition, their production being referred to certain physical 

 conditions attending some earlier period of the magma's existence. He 

 is inclined to regard their formation as influenced by water vapor at a 

 great pressure. 



Tliis same authority has also published* some interesting notes on the 

 nature and origin of the lithophyste and the lamination of acid lavas 

 as displayed in the obsidian of the Yellowstone Park. The ly thophysfe 

 he regards as of aqueo-igneous origin, as having been produced by the 

 action of absorbed gases ui)on the molten glass, from which they were 

 liberated during the process of cooling and consequent crystallization. 

 The differences in consistency and phases of crystalizatiou producing 

 the laminated structure are regarded as "directly due to the amount of 

 vapors absorbed in the various layers of the lava and to their mineral- 

 izing influence." 



In this connection a recent paper by Dr. A. Lagorio,t of the Uni- 

 versity of Warsaw, is of the greatest interest. The author gives tlie 

 results of several years' chemical investigation on the nature of the 

 glassy ground mass and crystallized portions of eruptive rocks and 

 arrives at sonic new and important conclusions. These, in brief, are as 

 follows: He considers the "normal glass," in which are dissolved all 

 the substances going on crystallization to form the crystalline secre- 

 tions of a rock, to be a silicate of the composition of K^O 2 Si 02 (l>' o08). 

 From this the dissolved oxides and silicates separate out in the order 

 of their solubility and the relative condition of saturation, the sodium- 

 bearing minerals, as a rule, separating out at an earlier stage than those 

 in which potassium is the predominating alkali. The order of crystal- 

 lization from the normal magma, as above given, would thus be as fol- 

 lows: Oxides, pure iron silicates, magnesian silicates, iron magnesian, 

 inagnesian lime, magnesian potash, lime, lime soda, soda, and finally the 

 potash silicates and free quartz. The writer states further that the 

 minerals forming the second generation of crystals are never absolutely 

 identical in composition with those of the first, and are dependent for 

 their formation not upon a recurrence of like conditions, but rather upon 

 the comi)osition of the residual magma. 



* Am. Jour. Set., 1887, xxxiii, pp. :3G-4r). 



t Ueber die Natur der Glasbasis sowio dor Krystallisatiiiusvorgliuge im eriiptiveu 

 Magma. Miu. u. pet. Mittli., 8. B., vi. H., 1887, p. 421. 



