192 I. Xo. 8. ON THE KCLOGITES Of^ NORWAY. 75 



After ha\ing stated that the kelyphitization, a change of pyrope and 

 olivine into pyroxene and spinel, is accompanied by increase of the mol. 

 \olume from 275 to 312.7, Mrha continues: 



"Der Granat ist als Erstarrungsprodukt flüssiger Magmen unter Atmo- 

 sphärendruck nicht bekannt. Zu seiner Bildung ist daher, wie auch aus 

 der Unmöglichkeit, ihn aus seiner Schmelze krystallisiert zu erhalten, her- 

 vorgeht, bedeutender Druck erforderlich. Der bei diesem Drucke vorhandene 

 Gleichgewichtszustand zwischen Pyrop und Olivin wurde jedoch gestört, als 

 das Olivinmagma, das die Pyrope enthielt, unter geringeren Druck gelangte. 

 Das Resultat dieser Störung war die Ausbildung einer Contactzone von 

 Mineralen mit grösseren Molecularvolumen." 



Similar formation of orthopyroxene and spinel round the garnet also 

 has taken place in the eclogite nodules in South Africa'. 



The Anipliiholitizatioii. 



The occurrence of amphibolitized border-zones round eclogites enclosed 

 in gneiss is a universal phenomenon in Norway as well as in other countries. 

 The breadth of the altered zones, in the occurrences in Nordtjord and 

 Møre, varies from a few centimeters to several decimeters and e\en metres. 



1 have seen large masses of amphibolite which enclose cores of eclogite 

 representing the last residues of the unaltered rock. 



This phenomenon was studied microscopically in specimens trom 

 Silden in S el je, collected by Dr. H. Reusch, and in my own specimens 

 from Bryggen. 



Megascopically the amphibolitized rock difters from the unaltered 

 eclogite by its dark colour. 



A specimen from Silden, representing a little advanced stage of 

 alteration, difters from the eclogites containing diopside-plagioclase symplec- 

 tite chiefly in the farther development of the kelyphite. It shows a diopside- 

 plagioclase-symplectite, in which the feldspar rods attain a breadth of 0,01 mm 

 and whose structure is in all respects identical with many examples described 

 in the previous chapter. There is no other difterence than a trace of uralitiza- 

 tion, appearing as a paramorphic change most advanced in the \icinity ol 

 the kelyphite shells. Most of the individuals of pyroxene have outer zones 

 of amphibole, but in others the amphibole occurs as enclosed spots. The 

 symplectic structure and the plagioclase rods remain unchanged in this 

 alteration. As the pyroxene and hornblende are seen in homoaxial growth, 

 both these may be easily determined from their extinction angles, the 

 magnitude of the axial angles and the optic character (in the pyroxene 



2 \' Y 60 +. in the amphibole 2 \' x = 75' ±1. The hornblende is 

 pale green in colour. A few larger grains of pale amphibole of earlier 



' Percy Wagner, op. cit. 1 Berlin 19091, p. loi. 



