OCCtTRRENCE IN ANCIENT BRITISH LATA8. 163 



paratively recent lavas. It appears that until 1860, certain un- 

 usually large segregations in the glassy rhyolites of Hungary had 

 been classed with ordinary spherulites. In that year, however, 

 Von Eichthofen, in his paper entitled " Studien aus den ungarisch- 

 siebenbiirgischen Trachjtgebirgen "*, considering that many of these 

 bodies were hollow in the centre, and in some respects resembled the 

 vesicles of scoriaceous lava, described them under the name of 

 " Lithophysen." He believed that inclusions or segregations of 

 highly siliceous matter had been, during the consolidation of the 

 lava, blown up into bladder-like forms by the steam that they con- 

 tained. The toughness of the surrounding glassy matrix prevented 

 the immediate escape of the steam, and caused these vesicles to 

 accumulate as hollow spheroids, their walls being formed from the 

 original segregated matter. When cut across, their cavities are 

 seen to be divided into chambers by dome-like lamellae, one above 

 the other, as if produced by successive expansions of the gas. In 

 some cases the solid part of the " Lithophyse " is in a loose and 

 powdery condition. The glassy matrix shows pronounced perlitic 

 structure, and is often reduced to a mere honeycomb by the abundant 

 development of the cavities. 



Szabo, however, in 1866 f, represented the hollow nodules as 

 nothing but altered spherulites, the removal of the material from 

 the interior, partly in solution, partly as fine powder, having left a 

 series of chambers which often follow the lines of the original con- 

 centric structure. He states that every successive stage of alteration 

 is to be found, and believes that a gradual concentration of silica 

 occurs in the layers that remain. These become finally strengthened 

 by a deposit of quartz-crystals upon their surfaces. 



It might still have been argued that the material found partially 

 or even completely occupying the centres of these Hungarian 

 spheroids was merely a product of infiltration ; but in addition to 

 chemical evidence given by Szabo, Karl von Hauer t published, a 

 few months later, analyses both of the ground-mass surrounding the 

 " Lithophysen " and of their contents. His results may be thus 

 compared : — 



Average of three Analyses Contents of the 



of the Grround-mass. Lithophysen. 



Silica 76-72 75-91 



Alumina 12*72 1 i /i q« 



Ferric oxide 1-80 J -^"^'^^ 



Lime 1-46 0-94 



Magnesia 0-26 0-34 



Potash 4-10 3-07 



Soda 2-88 3-36 



Loss on ignition .... 0*74 1-30 



99-90 



* Jahrbueh der k.-k. geol. Reichsanstalt, 1860, p. 180. 



t "Die Trachyte undRhyolite der Umgebung von Tokaj." Jahrb. der k.-k. 

 geol. Eeichsanstalt, 1866, pl^ 89. 



I " Die Gesteine mit Lithophysenbildungen von Telki-Banya." Yerhandl. 

 der k.-k. geol. Reichsanstalt, 186*6, p. 98. 



