CO ■ PF. NTT I F.SKOI.A. M.-\. Kl. 



'l"he surroundinj:^ gneiss cnibracxs numc rous lenses of the usual fine- 

 grained or medium-grained eelogite and is itself, in places, almandite- 



bearing. 



Theic is hardly any doubt of this coarse-grained and unequal rock 

 being analogous to true pegmatites and, on the other hand, to the amphi- 

 bole-eclogites desci-ibed above. In the present case the crystallization had 

 taken place within the temperature and pressure limits of the eelogite 

 faciès projjer, but the occurrence of the amphibole in the most pegmatite- 

 like portions proves that it was not far from the lower limit of this faciès. 



An occurrence of a somewhat similar, pegmatite-like eelogite was 

 described by G. Tschermak from Karstätten and (jurhof near Aggsbach in 

 Lower Austria ^ where eelogite is associated with olivine-rock and serpentine 

 in granulite. The eelogite contains: "faustgrosse Stücke von Granat, daran 

 zoUgrosse Omphazit- und Smaragditkorner und grosse Körner von Magnetit". 



Mineralogicai Varieties of Eelogite. 



The typical minerals of the eclogites present in all the structural 

 varieties are eel ogi te-gar n et and eel ogi te-cl i nopy roxene, the 

 specific distinctive characters of which have been discussed in "Mineral 

 Facies", pages 171 — 174. Typical minor constituents are rutile and 

 apatite, invariably present, and ilmenite and pyrite, very common. 



Eclogites exclusively composed of these type-minerals have been found 

 developed in the structural varieties i, 2, 3 and 4. 



Besides these typical constituents the eclogites frequently contain 

 amphiboles of the tremolite-actinolite-hornblende series, biotite, quartz 

 and pi agi o cl a se. We already touched on the problem of the rôle of 

 the amphiboles in the amphibole-eclogites. We found proofs in their struc- 

 tures indicating that the amphiboles are not congenetic with the other 

 minerals, although diey may be primary minerals in the usual sense, hav- 

 ing probabl}^ crystallized out from the magma. Yet they have originated 

 at the expense of earlier minerals and under other conditions than 

 the latter. 



In the eclogite-gabbro of the Romsdalshorn type the combination 

 hornblende-plagioclase plays very much the same rôle as the light-coloured 

 amphibole in the former case. 



Crystallization of amphiboles and amphibole-plagioclase mixtures may 

 also have taken place in a metamorphic way, by amphibolitization which 

 we shall find to be a phenomenon of uni\-ersal occurrence. The rock- 

 varieties thus developed are true alteration types whose existence depends 

 upon posterior changes. 



' G. Tschermak, Beobachtungen über die Verbreitung tics Olivins in Felsarten. Sitz-Ber. 

 Wiener Ak. Wiss. 1867, 56, I, 276. 



