286 Geological Society : — 



Some of the associated mica may be authigenous, but the author 

 believes much of it and other small constituents to be derivative. 

 There is, however, a mineral resembling a mica, exhibiting twinning 

 with (?) simultaneous extinction, which is authigenous. The knots 

 are merely matrix clotted together by some undefinable silicate, and 

 under the microscope have no resemblance to the " black garnets." 

 The prisms are much the same, but slightly better denned ; they 

 present no resemblance to the staurolites, but may be couseranite, 

 or a mineral allied to dipyre. Hence, though there is rather more 

 alteration in these rocks than is usual with members of the Mesozoic 

 series, and an interesting group of minerals is produced, these 

 so-called schists differ about as widely as possible from the crystalline 

 schists of the Alps, and do not affect the arguments in favour of the 

 antiquity of the latter. In short, they may be compared to rather 

 poor forgeries of genuine antiques. Incidentally the author's 

 observations indicate (as he has already noticed) that a cleavage- 

 foliation had been produced in some of the Alpine schists anterior 

 to Triassic times. 



February 5.— W. T. Blanford, LL.D., F.E.S., President, 

 in the Chair. 



The following communications were read : — 



1. " The Yariolitic Rocks of Mont-Genevre." By Grenville A. 

 J. Cole, Esq., F.G.S., and J. W. Gregory, Esq., F.G.S., F.Z.S. 



The following conclusions were arrived at by the authors as the 

 result of their observations : — 



The gabbro or euphotide south of AIont-Genevre is associated with 

 serpentines, which were originally peridotites, and were not derived 

 from the alteration of the gabbro. These coarsely crystalline rocks 

 probably form a considerable subterranean mass, but have little 

 importance at the surface. 



They were broken through by dykes of dolerite and augite-ande- 

 site, and are now overlain by a great series of compact diabases and 

 fragmental rocks, which has no direct connexion with the gabbro. 



The Yariolite of the Durance occurs in situ as a selvage on the 

 surfaces of contact of these diabases among themselves, as blocks 

 in certain fragmental rocks, which are regarded by the authors as 

 tuffs, and occasionally as a selvage to the diabase dykes. 



This product of rapid cooling was originally a spherulitic tachy- 

 lyte, and has become devitrified by slow secondary action. Yariolite 

 thus stands in the same relation to the basic lavas as pyromeride 

 does to those of acid character. 



The eruptive rocks in the Mont-Genevre area are probably Post- 

 Carboniferous, but their exact age cannot at present be determined. 



There are several other areas of similar variolitic rocks among 

 both the Alps and the Apennines of Piedmont and Liguria. 



The best modern representatives of the conditions that produced 



