Chapter IX. 

 DISCUSSION AND CONCLUSIONS. 



In bringing these studies to a close we must comment upon certain problems which have 

 arisen in connection with the features we have described. 



THE GREEN-ROCKS OF THE ALPINE TYPE. 



Great difficulties still remain in regard to this series of rocks and the reconciliation of their 

 diverse characters. Considering first the chemical characters of these rocks we find that the 

 Italian analyses (all "inferior" according to Washington '03, '04) indicate that the green-rocks 

 are all of normal alkali-calcic composition, with the exception of a mica-teschenite (Verri '00). 

 Strong sodic solutions were, nevertheless, emitted from them, for the marls have been ex- 

 tensively albitized along their contact with the diabases, and in one instance a radiolarian 

 cast was found preserved in a crystal of albite (Issel '90). In some Swiss types, more 

 soda is present. The rocks of the Bagnetal, if they are rightly considered in this con- 

 nection, are in composition intermediate between basalt and trachydolerite, soda and tita- 

 nium being noteworthy (Woyno '11). Those near Brig (Preiswerk '07) and in the Julier Pass 

 (Upper Engadine) (Cornelius '12), show a higher content of soda, some types approaching the 

 composition of keratophyre, while Grubenmann ('09) has called attention to the "essexitic" 

 character of those of the Lower Engadine. Thus, particularly in the occurrence near Brig, 

 there are chemical features which are comparable with those of the spditic suite, though in 

 some analyses cited by Grubenmann there is a suggestion of a secondary alteration of composi- 

 tion comparable with that investigated by Termier ('98), an elimination of lime with some 

 addition of soda. How far this process may have affected the whole series is not clear. These 

 alkaline characters are seen in the diabasic types, including some coarse-grained specimens 

 referred to gabbros in the Brig area (see p. 27), but they are generally absent from the gabbros 

 proper, the gabbro-schists, and allalinites. 



In regard to the mode of occurrence, while no indubitable volcanic rocks are known * 

 (Suess IV, p. 134) the pillow-lavas indicate rapid chilling, and may have resulted from intrusion 

 into unconsolidated submarine sediments. On the other hand the peridotites and schistose 

 gabbros are clearly plutonic in petrographic character. Considering first the finer-grained 

 types apart from the gabbros, the Italian geologists believe them to be flows interbedded with 

 the Eocene marls in the Apennines showing intrusive features owing to the unconsolidated 

 nature of the sediments over which they flowed. 2 The Piedmontese pietre verdi are believed 

 to be flows of various ages between Permo-Carboniferous and Jurassic. Termier ('98) considers 

 the greenstones of Pelvoux Triassic flows, and Zaccagna ('87) so explains the variolite and 

 spheroidal diabase of Monte Viso. Schmidt and Preiswerk ('08) found the green-rocks of the 

 Simplon area to appear as if they were interbedded flows on either side of the boundary between 

 the Triassic dolomite, and the Jurassic calc-phylhte, quite unconnected with the folding. The 

 same conclusion was reached by Seidlitz ('06) in the Engadine and Meyer and Weber ('10) in 

 the Tauern. Other workers in the Engadine have come to different conclusions. Cornelius 

 ('12) held that the green-rocks of the Julier Pass were injected into their present position during 

 the Tertiary folding. Lorenz ('02) has similarly explained the green-rocks of the southern 



i "It still remains to be determined by extensive research whether a true volcanic action was associated with the intrusion of the ophiolites, 

 whether there were produced as a result of submarine extrusion the peculiar features like pillow-structure, and the peripherally vesicular character 

 of the pillows, and how far the dislocations have obliterated the originally effusive character'* (Steinmann '05, p. 57). At Monte Genevre, Cole and 

 Gregory ('90) believed tuffs were developed, and Woyno CU) considers the prasinites and glaucophane-schists of the Bagnetal have resulted from 

 the metamorphism of lavas and tuffs in the Mesozoic calc-phyllites. For a recent discussion of the significance of pillow-structure see Lewis ('14). 



3 See also Stefani ('13). Sacco ('05) and Steinmann ('05) contend the marls and radiolarite are not Tertiary but Cretaceous or older. 



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