'2'A') v. K. WRKUIT OBSIDIAN FROM ICELAND 



ill accord as to the genesis of the lithophysae. Yon Eichthofen had 

 •suggested in 1860 the name Lithophysen' (Greek Xl6o<;, stone, and <l>vaa, 

 ■l)ubhle) for the hollow spherulites m the Hungarian rhyolites, on the 

 assumption that their formation is due to the expansion of gas bubbles 

 which, liberated during the crystallization of tlie spherulites, are unable 

 to escape from the viscous magiiia and lience force out the walls of a 

 cavity, each successive bubble carrying a thin film (bubble) or shell of 

 the magma into the cavity, and thus producing the concentric structure. 

 During this process chemical reactions between the gases and the crystal- 

 lized material of the spherulites take place and cause solution, reciys- 

 tallization, and a general rearrangement of the original material pre- 

 cipitated from the magma. Zirkel'* in 1876 practically adopted von 

 liichthofen's hypothesis of chemical alteration. S. Szabo'^ and Eoth,*^ on 

 'the other hand, considered that the lithophysa^ are tlie result of chemical 

 and mechanical alteration of solid spherulites, the solul)le portions being 

 removed chemically, the insoluble mechanically, with the exception of 

 silica, which constitutes the major part of the lithophysa?. This view 

 involves transfer of material away from the cavity, wJiile according to 

 von -Richtliorcirs idea there is no such transfer, only rearrangement 

 within the cavity. Still other views were held by von Hauer' and AVeiss,® 

 Avho considered that lithophysai are linllow s])h('rnlit('s fdrnicd about the 

 gas bubbles which escape from th(> coDJiiig mauina. ('I'oss" concluded 

 from his study of litho])hysa? that the minerals. t()])az and garnet, which 

 occur therein, were '"produced by sublimation or crystallization from pre- 

 sumably heated solutions, contemporaneous or nearlv so with the final 

 consolidation of the rock. The litho])hysal cavities seem plainly caused 

 by the ex])ansive tendency of confined gases or \apois. while the shrinkage 

 cracks in the walls and white masses of (he Xathvo]-) I'ock suggest the 

 former presence of juoisture." 



Iddings found "that the lithophysae in the obsidian of Obsidian Cliff, 

 with their contents of prismatic quartz, tridyniite, adnlar-like and tabular 

 soda-orthoclase, magnetite and well ciwstallized fayalite, are of aqueo- 

 igneous origin, and result from the action of absorbed vapors on the 

 molten glass from which they were liberated during the jirocess of crvs- 

 tallization consequent upon cooling."" An arching of the la vers around 



3 Jahrb., K. K. Geol. Reichsanstalt, vol. 11. 1860. p. 181. 



^ tT. S. Geol. BxpL. 40th Parallel, vol. 6 ; Microscop. Petrography, 1876. p. 212. 



= Jahrb., K. K. Geol. Reichsanstalt, vol. 16, ISGfi. p. S9. 



" Beitrage zur Petrographie der pliitonischeu Gesteine. 1860. p. 16S. 



' Verhandl. K. K. Geol. Reichsanstalt. 1866, p. 08. 



8 Zeltschr. Deutsch. geol. Gesellschaft, vol. 20. 1877. p. 418. 



»Am. .Tour. Sci. (3), vol. 31, 1886. p. 432. 



