ON THE VAEIOLITIC ROCKS OF MONT GENEVKE. 297 



his collection from Mont Genevre was described by Delesse * ; 

 Scipion Gras certainly examined it in situ^smd inconsequence denied t 

 the volcanic origin of either the variolite or any of the rocks asso- 

 ciated with it. 



Delesse's memoir " Sur la variolite de la Durance " t was the 

 first serious attempt to treat the rock from a modern point of view ; 

 the paper was illustrated by a coloured plate, which was supple- 

 mented by an exquisite lithographic drawing in the same author's 

 " Recherches surles roches globuleuses " §. Delesse was led by his 

 examination of the collection and acceptance of the field-work of 

 M. Elie de Beaumont to accept the passage from euphotide to ser- 

 pentine, and to regard the variolite as a selvage to the euphotide. 



Supplementing the laboratory-researches of Delesse, Lory made 

 in the field a series of observations which have long appeared to be 

 conclusive. In 1861 the Geological Societj^ of Prance, under his 

 guidance, spent one day in the variolitic area ; visiting the Col du 

 Gondran, they saw the largest gabbro mass, and having probably 

 met with this rock again in the Chenaillet Valley, they greatly 

 exaggerated its importance ||. Lory argued on that occasion, in 

 opposition to M. Hebert, that the melaphyre-like rock was only an 

 " euphotide porphyroide, comme la variolite serait une euphotide 

 globulaire," and that the latter was a structural modification of the 

 gabbro on its selvages. These views Lory indicated clearly in 1863 

 in his map and sections of the Brianconnais ^ ; in the latter he repre- 

 sented this igneous massif as composed of euphotide intrusive in the 

 surrounding schists, and with a selvage of variolite on the west and 

 of serpentime on the east. In 1861 he repeated these views in a 

 rather detailed account of the area in question ** ; in his well-known 

 memoir he reaffirmed the passage from euphotide to serpentine on 

 the one hand and to porphyry and variolite on the other tt. 



The first application of the microscope to the study of thin sections 

 of the variolite of the Durance was made by Inostranzev in 1874, 

 in his valuable paper " Variolitye " :J:J, in which he described in 

 detail the variolite of a new locality, Yalguba in 01onetz,and devoted 

 several pages and figures to the microscopic structure of that of 



* Ann. Mines, ser. 4, t. xvii. p. 130. 



i' Gras, Sc, " Introduction a, un Essai sur la constitution geologique des 

 Alpes centrales de la France et de la Savoie," Bull. Soc. geol. France, 2""^ 

 s6r. t. i. pp. 723-4. 



I Ann. des Mines, ser. 4, t. xvii. pp. 116-131, pi. i. Comnt Rend. xxx. 

 pp. 741-743 ; Bull. Soc. geol. Fr. 2'"'= ser. t. vii. pp. 427-431. 



§ Mem. Soc. Geol. Franc, 2'"« ser t. iv. (1852) pi. xxiv. if. 18-20. 



jl "Reunion extraordinaire a Sc. Jear, de Maurienne," Bull. Soc. geol. France, 

 2'^'" ser. t. xviii. pp. 779-784. 



^ " Carte et coupes geologiques du Brianconnais," Bull. Soc. geol. France, 

 2""^ ser. t. XX. pp. 233-235, pis. iii. & iv. 



** Lory, " Description geologique du Dauphine," Bull. Soc. Statistique de 

 risere, ser. 2, t. v. (1861) pp, 1-240, pi. i. ; ser. 2, t. vi. (18(U) pp. 1-260, 

 pis. ii., iii. ; s6r. 2, t. viii. (18()4) pp. 7-252. 



ft Loc. cit. par. 293 ; Bull. Soc. Stat. Isere, ser. 2, t. vii. p. 86. 



\\ Verb. russ. k. min. Ges. St. Petersburg, ser. 2, Bd. ix. (1874) pp. 1-28, 

 pis. i., ii. 



x2 



