GEOLOGY OF THE WESTERN ALPS. 171 



less altered basic igneous rocks, but their aoe seemed 

 very uncertain, for the evidence was contradictory. The 

 authors now show that there is a treble series of basic 

 igneous rocks in this district. The first occurred between 

 the periods of the " schistes lustres" and the Trias, for the 

 rocks are intruded through the former, and fragments of them 

 occur in the Trias. A second series is post-Triassic and 

 pre-Cretaceous, for it cuts through the former, and not the 

 latter. The third, including the Variolitic rocks of Mount 

 Genevre, and the associated rocks, is probably Lower 

 Cretaceous. 



In connection with this subject we must welcome a 

 paper in which some very important sections near Genoa 

 are again described. For though these are not in the 

 Western Alps they have exercised a considerable influence 

 on the theories regarding the age of the igneous rocks of 

 the '' pietre verdi " in them. Mazzuoli and Issel (described 

 these in 1884 in a paper entitled "Sulla zona di coincidenza 

 delle formazioni ofiolitiche eocenica e triasica della Liguria 

 occidentale V Their.map showed two series of the " pietre 

 verdi," one in Triassic, and the other in Eocene rocks. 

 The igneous series were parallel to one another, whereas 

 the two sedimentary series were unconformable. It was 

 therefore suggested by two authors that the two sets of 

 igneous rocks were really part of the same series. In this 

 they assumed the eruptive origin of the "pietre verdi," 

 just as the Italian authors had assumed that these were 

 altered bedded sediments. Signor Mazzuoli (13) has now 

 returned to the subject, and stated his views in greater 

 detail. He again urges that the serpentines in the Eocene 

 rocks of Northern Italy are mainly the result of the altera- 

 tion of a lherzolite at the time of its eruption. The 

 euphotide and diabase, on the other hand, the author claims 

 to be the result of the alteration of a sedimentary rock ; he 

 declares they were originally a marl, which had been de- 

 posited at a considerable depth below the sea ; this was 

 traversed by gases and liquids containing silicic acid. The 



1 Boll. R. Com. Gcol. d'llal., vol. xv., p. 2. 



