330 MESSES. G. A. J. COLE AND J. W. GREGORr 



wald, and Voigtland, and doubtfully those of the Durance ; the 

 second division, or the spherulitic augite-porphj-rites, is constituted 

 by the variolites of Yalguba and some described by Geinitz. As will 

 have been seen by our previous description, the variolites of Mont 

 Genevre mainly belong to the second class. 



Owing to the looseness with which the name " variolite " has 

 been used, it will be advisable in this connexion to repeat our 

 definition of the term, although from the modern point of view 

 the rock would scarcely require a distinctive name. As the 

 variolite of the Durance was the first scientifically studied and 

 described, we think it ought to be regarded as the type, in preference 

 to the obscure " Variolites Lucernensis," or the unknown Italian 

 rock described by Aldrovandus. We therefore define " variolite " 

 as a devitrified spherulitic tachylyte, typically coarse in structure. 



The unaltered rock that is probably most closely related to 

 variolite is the spherulitic augite-andesite of the Vashegy mountain 

 near Telkibanya, in Hungary. For interesting information re- 

 specting this rock we are indebted to Dr. J. de Szadeczky, of 

 Budapest. 



The variolite of Yalguba, iii Olonetz, also closely approaches that 

 of the Durance, and is of interest from the occurrence in the 

 matrix of small patches of a brown glass which have escaped 

 devitrification. This rock has been described in considerable 

 detail by Inostranzev* in 1874, by Loewinson-Lessing f in 1884, 

 and again by the latter author in his elaborate memoir " Olonetz- 

 kaya Diabazovaya rormaziya"i. Lcewinson-Lessing seems in- 

 clined to abandon variolite as the name of a rock-species in favour 

 of spherulitic augite-porphyrite, retaining it, however, in the form 

 of " variolitism " for that of a process §. As variolitization seems 

 to have resulted from the same causes that have built up ordinary 

 spherulites, we do not see the necessity for the new term, especially 

 as its introduction would obscure the identity of the results that 

 have been produced by the action of similar causes on both the acid 

 and the basic rocks. 



The above definition of variolite, however, excludes several rocks 

 that have been regarded as variolite ; thus, that found by Dathe|| 

 in the Culm Conglomerate of Silesia contains 75 per cent, of silica, 

 and certainly cannot be regarded as a basic rock, unless a considerable 

 proportion of the quartz is secondary. The close association of this 

 variolite with gabbro and gabbro-conglomerate suggests that such 

 may be the case, though Dathe has abandoned his original view of 

 the connexion of the variolite and gabbro. Neither do we see any 



* A. Inostranzev, "O Variohtye," Verb, k, russ. min. Ges. St. Petersburg, 

 1874, pp. 1-28, pis. i. & ii. 



t F. Loewinson-Lessing, Tsch. Min. u. petr. Mitth. vi. (1884) pp. 281-300, 

 pi. iv. 



t Trud.St.Petersburgskagho Obshch. Estest. xviii. (1888) pp. 29-396, pi. i.-v. 



§ Ibid. p. 169. 



II J. Fr. E. Dathe, Jahrb. k. k. preuss. geol. Landesanst. fiir 1882 (BerUn, 

 1883), p. 254. 



