24 BASIC AND ULTRABASIC IGNEOUS ROCKS— BENSON. [MEM0,BS [^xit 



ITALY. 



The range then continues to Italy, where gabbro and serpentine appear in the ancient 

 rocks of southern Calabria. Lovisato ('78) compared these with the green-rocks of northern 

 Italy and was supported by Novarese ('06). Tilmann ('12) suggests that they are the roots of 

 the green-rocks in the Eocene formations of northern Calabria. 



The green-rocks appear again in the neighborhood of Florence, whence they stretch in a 

 series of intrusions through the Tuscan Sub-Apennines (Catena Metallifera) and the Ligurian 

 Alps, and sweep in great masses into the Maritime Alps, and especially the Piedmontese Alps. 

 They also occur in Elba and Corsica. The problem of the origin of these rocks has long been a 

 battleground for geologists, and the most diverse views are held even to the present. The 

 following remarks are based upon the account given by Suess (IV) and (what appears to be 

 more in accord with the views of Italian geologists so far as the writer has been able to ascertain 

 them), the recent review of Preller ('18) in which numerous important papers are cited. 3 The 

 reason for the great diversion of opinion is the exceedingly disturbed character of the rocks, so 

 that it is not clear whether the green-rocks are a series of contemporaneous flows and intrusions 

 in moderately displaced but still autochthonous formations (the Italian view), or have been 

 passively moved hither and thither in a series of immense sheet-folds rooting in the Dinaric 

 Alps, or in Corsica, and are thus largely exotic (the view of Steinmann ('07, '13), who holds 

 the serpentine, etc., are entirely of Jurassic age, of Termier ('10, '12). and their followers), or 

 whether they have been injected into the weaker formations during immense overthrus tings 

 (Suess IV) . According to the Italian geologists the ophiolitic rocks of the Tuscan Sub-Apennines 

 are lenticularly infolded in the Eocene sediments; they show no evidence of angular intrusion, 

 apophyses, or contact-metamorphism, but were a series of submarine lava-flows which became 

 incorporated in the plastic sediments. Not unfrequently the spheroidal pillow-structure is 

 visible in the diabasic rocks (Mazzuoli and Issel '81, Delkeskamp '07), even when they have 

 been altered to felspathic amphibolite or prasinite. There are no visible channels of eruption. 

 The sediments with which they are interbedded are mostly somewhat siliceous limestones, 

 often nummulitic, passing into calcareous chert, "diaspri," containing radiolaria. In the 

 larger intrusive masses the superposition of the principal basic rocks in differentiated areas show s 

 almost invariably a basal laj r er of serpentine followed by gabbro and felspathic diabase. Daly 

 ('14, p. 449) cites a clear illustration of this feature. In rare instances gabbro is absent and dia- 

 base overlies serpentine directly. Nevertheless the serpentine frequently contains veins and 

 intercalations of gabbro, less frequently of diabase, which on the other hand invades gabbro. 

 Preller adds: "This order of superposition and intercalation corresponds to the order of eruption 

 and consolidation from essentially the same magma, which also produced the occasionally 

 associated granitic rocks as acid concentrations." 



It will be useful here to cite Suess's brief summary (IV, p. 147) : 



In the Apennines the green-rocks of the Alps are repeated chiefly in the Cretaceous, Eocene, and Oligocene (or 

 Upper Eocene) beds as in Corsica. On the Middle Trebbia, where they are not older than Oligocene, Traverso distin- 

 guishes a series of igneous rocks, which has arisen from the differentiation of a common magma. The first products 

 gave rise to Iherzolite and serpentine, the second to gabbro and diabase, the most recent to granite. The granite occurs 

 only in limited areas, generally as veins. In Elba the granite makes its appearance in greater mass, and there, too, rep- 

 resents a comparatively late product. The green-rocks are transformed by contact with it into alternating layers of 

 hornblende-schist and enstatite-serpentine. This granite is younger than the folding of the Apennines. 



The divergence of interpretation is very marked in the case of Elba, where, in opposition 

 to Termier's ('10) "geopoetic" conception of three immense recumbent sheets, the lowest 

 thrust subterraneously from the Dinaric Alps 300 miles to the east, Lotti ('10), followed by 

 Preller, considers the formations are autochthonous. The submarine eruptions of diabase and 

 variolite occurred in Early and Middle Eocene time, and are associated with very silicified red 

 calcareous radiolarian chert resulting from the alteration of limestones by silico-ferruginous 

 solutions from the basic lavas. The abundance of these waters is indicated by the fact that 



• An exteusivo bibliography of the Italian "pietre vtrdi" is given by Franchi ('10). 



