academy of sctences] ALPINE AND ATLAS MOUNTAINS. 25 



the cherts are at least as extensive as the igneous rocks. In the later Eocene and Miocene 

 times there was a general upheaval and folding with the intrusion of laccolitic masses of acid 

 porphyry and granite. 



On the mainland tracing the sequence further to the north, the Ligurian Apennines are 

 found to show many features similar to those already described. Serpentine, compact, schis- 

 tose, or porphyritic, is associated with gabbro (euphotide) and diabase, but there is no passage 

 from serpentine into the two latter rocks, between 'which there are often transitions. They 

 are associated with silico-calcareous greenish and reddish schist containing radiolaria, and 

 forming bands on the margin of ophiolitic rocks in the neighborhood of calcareous deposits. 

 They are stated to be of Upper Middle Eocene age and rest on Middle Eocene sandstone. 



In the west of Liguria the Alps and Apennines come into contact. The Eocene pietre 

 verdi or green-rocks are brought into contact with a Triassic series of similar origin, but rather 

 different facies, being dark blue limestone and calc-schists, which, with the exception of some 

 small occurrences in Elba, are the southernmost portions of the great series of Mesozoic rocks 

 with intercalated green-rocks that play so prominent a part in the composition of the Maritime 

 and Piedmontese Alps. Here, too, we find a marked divergence between the explanations 

 given: the essentially autochthonous character of the formations in Western Liguria, though 

 with minor overthrustings, is supported by Rovereto ('09), Preller ('18), and the weight of 

 Italian geologists, while that they are immense exotic sheets is suggested by Termier and 

 Broussac ('12). 



The structure of Corsica indicates that it is a southern spur from the Piedmontese Alps. 

 There is, however, still considerable doubt as to the structure of the island. With the highly 

 folded ancient Mesozoic and Tertiary rocks there are intrusions of peridotite, norite, gabbro, 

 diabase, and particularly serpentine which occur just as they do in the Alps. Maury ('03), 

 whose view, is accepted by Suess, states that they penetrate as far up as the Oligocene Flysch, 

 and are overlain by the first Mediterranean stage, but Rovereto ('05) holds that they are older 

 than the Rhaetic, though younger than Middle Trias and occur among Triassic calc-schists. 



The modern views of the nature of the green-rocks in the Piedmontese arc of the Alps are 

 due in very large measure to the work of Franchi, together with Novarese and Stella (Franchi 

 '98, '04, Novarese '95). Omitting reference to the Ivrea zone of intrusions the following 

 appears to represent the view generally accepted by Italian geologists. The green-rocks ap- 

 pear at all elevations throughout the regions; except in the prevalence of green-rocks with un- 

 altered minerals in Permo-Carboniferous mica-schists, and those more altered in the Liassic 

 calc-schist, there seems to be no regular order of succession, superposition, or distribution among 

 them. In the mica-schists they appear not as irruptive angular injections with apophyses, but 

 as lenticular concordantly stratiform masses, that, owing to the differential crushing, show 

 pseudo-intrusive phenomena. There are frequent passages between the several types of erup- 

 tive rocks 4 but there is no conclusive evidence of contact-alteration. This close association of 

 rocks of different origin is considered to be the result of repeated penetration of eruptive viscid 

 lavas into the sedimentary deposits in the course of consolidation. Sometimes in the less 

 metamorphosed regions, as at Monte Genevre, one may see the pillow-structure perhaps formed 

 in the variolitic consolidations of the magma as it was injected into watery silt, and quite ad- 

 jacent to these appear coarse-grained gahbros (euphotides) (Cole and Gregory '90). Altered 

 pillow-lavas also occur with diabase and amphibolite-schists at Monte Viso (Zaccagna '87). 

 In neither horizon do these appear as deep-seated rocks; they are on the contrary associated and 

 interstratified with the other green-rocks at all levels, overlying and underlying, and intercalated 

 in them and the crystalline schists. All green-rocks are of more or less altered condition, and 

 the schists formed from them present the usual actinolitic, glaucophanitic, zoisitic, chloritic and 

 talcose varieties, while garnetiferous types tending to eclogites are also present. They all 

 may exhibit a marked tendency to chloritic decomposition, which applies even to the Iherzolites 

 and associated euphotides. This process is much less in evidence in the green-rocks of the older 

 or mica-schist formation than in the younger or calc-schist formation, for the former are much less 

 permeable and contain less magnesia than the latter. 



1 See e. g. Zambonim's ('06) detailed account. 



