Orenvilie A. J. Cole — Rhyolites of the Vosges. 301 



presence of a coarse granophyric structure. Under the microscope^ 

 however, while the red rays resemble in constitution the ordinary 

 spherules, the intervening matter proves to represent the matrix, 

 now petrosiliceous, it is true, but retaining the characteristic perlitic 

 curves, marked out often by ferruginous stains and granular products 

 of alteration. The sisherulites are, in fact, imperfect, being con- 

 structed of radially-grouped rods, circular in cross-section, stretching 

 outwards from a more compact and normal centre. That tlie alter- 

 nating and more transparent layers consist, not of original quartz, 

 nor chalcedony, but of a devitrified glassy matrix, the specimen 

 figured leaves, I think, no room for doubt. (Fig. 2.) 



Further alteration might convert this material into the semblance 

 of chalcedonic veinules, or might even replace it by bands of 

 secondary quartz. The frequent mention by older writers — Mon- 

 teiro,^ for example — of interlamination of "quartz and felspar" in 

 the nodules of pyromerides makes one certainly prepared for the 

 development of granophyric structure in such masses on a handsome 

 scale. Delesse ^ even held that the " quartz " in the rock of 

 Wuenheim exerted some influence on the globular forms of the 

 spherules at the time of their development, and that the alternating 

 bands were due to a primary separation of the constituents. But in 

 another place ^ he shows that the more siliceous fibres are probably 

 chalcedonic, since the etching of polished surfaces of the rock with 

 hydrofluoric acid destroys them more rapidly than the felspathic rays. 

 M. Michel Levy,* accepting the siliceous rays and veinules in the 

 pyroraeride of Gargalong as consisting of chalcedony, believes thera 

 to be primary, and to characterise a distinct type of rock, peculiar 

 to Permian and Triassic days ; that is, a rock intermediate in 

 structure between the micropegmatites with their radial quartz and 

 the modern lavas with spherules largely made of opal. 



The example from Wuenheim, however, recalls forcibly a structure 

 occurring in glassy rocks of comparatively recent date. Yon Eicht- 

 hofen ^ noted in the perlites of Tolcsva and Erdobeuye in Hungary 

 certain groups, one or two inches across, of radially divergent rays, 

 interpenetrated by the homogeneous magma, and regarded them as 

 coarse spherulites extended outwards in this open fibrous manner 

 until they were checked by coming into contact. Vogelsang,^ seek- 

 ing for an explanation of this abnormal mode of growth, observed 

 that the general direction of flow of the rock, as indicated by the 

 lines of trichites, was the same in the spherulitic rays as in the 

 matrix, but that local disturbances in this arrangement occurred in 

 the glassy interspaces, where the trichites seemed even to follow the 

 outlines of the several rays. He was thus led to the conclusion 



^ Journal des Mines, tome xxxv. (1814), pp. 347 and 407. 

 ^ Bull, de la Soc. geol. de France, tome ix. p. 177. 

 ' Mem. de la Soc. geol. de Fr. 2me serie, tome iv. p. 313. 



* Bull, de la Soc. geol. de Fr. 3me serie, tome iii. (1875), p. 226. Cf. Noury. 

 " G^ologie de Jersey," p. 33. 



^ Jahrbucli der k.k. geol. Eeichsanstalt, vol. ix. (1860), p. 180. 

 ^ Die Krystalliten, p. 148 ; also plate xvi. fig. 1. 



