324 Reviews — Prof. Stefani — Eruptive Rocks of the Apennines. 



mistaken the bastite and enstatite for diallage ; (3) from enstatite or 

 other pyroxene in cases where there seems no trace of olivine 

 (Cossa) ; (4) a theory attributed to (but already promptly repudiated 

 by) Mazzuoli of the formation of olivine, etc., by the dehydration 

 of serpentine. Finally, the author does not regard as reliable the 

 method proposed by Hussak for distinguishing serpentines formed 

 from rhombic pyroxenes from those formed from olivine (p. 19(5). 



§ 3. The Gabbro. — This term is adopted instead of eupkotide, 

 which has been much used by Italian geologists owing to the mis- 

 application of the former by Savi. A petrosilex or forellenstein is 

 formed locally by the segregation of the labradorite, and a diallagite 

 by that of the pyroxene. The gabbro is also at places altered to 

 " thulite " by the loss of silica and addition of magnesia. There 

 are many alteration products present, including some serpentine ; 

 but this the author regards as indicating that the rock was there an 

 olivine gabbro, rather than the formation of the serpentine from 

 diallage. 



Norites have been quoted from the district only owing to the 

 diallage having been mistaken for hypersthene. 



§ 4. Diabase is extremely abundant ; amygdaloidal and variolitic 

 structures are common ; in opposition to the opinion of Eosenbusch, 

 Gumbel, etc., the author does not regard the latter as a mere contact 

 phenomenon. True diorite does not' occur, but the uralitization of 

 the augite is often so complete that it is then almost impossible, 

 as at Eiparbella, to be certain that the rock is really an epidiorite. 



§ 5. A soda granite is fairly widely distributed in Emilio and 

 Liguria di Levante, and this Prof. Stefani regards as having 

 probably been a liparite. 



§ 6. Certain diabases and serpentine breccias have been previously 

 described, as e.g. by Prof. Bonney from Levanto. These the author 

 regards as " tuffs " analogous to those that accompany the 

 "kimberleyite" of S. Africa, and the picrites of the Ficktelgebirge. 

 Sometimes, as Mulino di Villa, the tuffs include diabase fragments 

 with variolitic surfaces ; Prof. Stefani regards these crusts as due 

 to the decomposition of the diabase, though it may be suggested 

 that they are really variolitic tuffs like those simultaneously described 

 from Mont Genevre. Similarly the rock from Levanto, re-described 

 as an " ophicalcite tuff," seems very much like the rock from Mont 

 Genevre, regarded as a serpentine breccia. 



§ 7. In discussing the. eruptive origin of the rocks, the author lays 

 much stress on the salbands, which he regards as conclusive in the 

 case of the diabase. Much value is also attributed to the amygda- 

 loidal and porphyritic structures. The other theories, such as 

 Mazzuoli and Issel's " anfimorphic " hypothesis (that the serpentines 

 have resulted from the alteration of a hot, submarine mud), and 

 Taramelli's view of the formation of the same rock as a precipitate 

 in a hot sea, are examined and dismissed. Prof. Stefani claims that 

 all the rocks are eruptive, and that the coarseness of grain of the 

 gabbro is due to its having arisen as an outpouring on the floor of 

 a deep ocean and having solidified under the enormous pressure of 



