ON- THE VAEIOLITIC EOCKS OP MONT GBNEVRE. 323 



here traced portions of the two first-mentioned maps, which will 

 illustrate the position better than any words * (figs. 7 & 8). 



Prof. Bonney f also declines to accept the " schistes lustres " as 

 Triassic. He regards them as schists which have retained their 

 original stratification, and as forming the uppermost member of his 

 three Archrean groups. If, then, the euphotides and diabases are 

 subsequent to the " schistes lustres," they may still be of very con- 

 siderable geological age. 



At its northern end, however, the variolitic series of Mt. Genevre 

 abuts against a normal compact limestone, the " Calcaire du Brian- 

 connais," which is certainly above the horizon of the anthracitic 

 Carboniferous strata. Accurate palaeontological evidence being 

 still wanting, even on Mt. Chaberton, we cannot state with cer- 

 tainty that this limestone is either Triassic or Liassic, but we 

 believe with Lory that our series has been erupted through it, as 

 well as through the dubious " schistes lustres " or " calcescisti " of 

 Zaccagna. The eruptive group has suffered from folding, faulting, 

 and in some places from brecciation ; but the earth-movements 

 that took place in this area at the close of the Eocene period would 

 amply account for these phenomena. In fine, we observe that 

 throughout Liguria and the western Alps the distinction between 

 the pre-Tertiary and Eocene serpentinous groups is becoming a 

 matter of pure stratigraphy J. The existence of, at least, two 

 groups has been again and again accepted ; but, in the absence of 

 the direct evidence afforded by the presence of derived pebbles of 

 these rocks in subsequent formations, the age often assigned to the 

 older masses may be looked upon with considerable caution. The 

 admitted exact resemblance of the igneous rocks themselves at 

 different horizons makes the most careful investigation all the more 

 desirable before an age is affirmed in any instance. As long as the 

 view that diorite, euphotide, and serpentine are formed by meta- 

 morphism from contemporaneous muds continues to be prominently 

 put forward, so long must the true stratigraphical position of Italian 

 and Alpine " greenstones " be involved in considerable obscurity. 

 While we may accept with Lory a maximum age for those of 

 Mt. Genevre, we must in fairness merely style them Post-Carhoni- 

 ferous until further evidence is forthcoming. 



IX. Conditions of Formation. 



In dealing with the question of the physical conditions that gave 

 rise to the variolitic series and its associated rocks, it is only fair to 



* It is unfortunate for purposes of refei-enee that the topogi'aphers have in 

 GastakU's map written " Mt. Genevre " in place of " Clavieres," while preciselj'- 

 the reverse mistake has occurred in that of Zaccagna and -Mattirolo. In our 

 copy from the latter the name is omitted, the frontier being sufficient guide. 



t " On two Traverses of the Crvstalline Rocks of the Alps," Quart. Journ 

 Geol. Soc. vol xlv. (1880) pp. 9() and SO. 



\ See, for example, Mazzuoli and Issel — " Sulla zona di coincidenza delle 

 formazioni ofiolitiche eocenica e triasica della Liguria occidentale," Boll. R. 

 Comit. geol. d'ltalia, vol. xv. (1884) p. 2. 



