I92I. No. 8. 0\ THE ECLOGITES OF NORWAY. 45 



The garnet is brownish red in colour. It contains a few inckisions, 

 some of which are rounded and may be quartz, whilst other are small 

 prisms with high birefringence, probably rutile. 



The pyroxene is pale green of various intensity and with no notice- 

 able pleochroism. 2\'y about 50 . This mineral shows a myrmekite-like 

 intergrowth with plagioclase (fig. 5, pi. II. 



The hornblende is chiefly found as groups of small crystal grains 

 around the pyroxene. Its colours for ß and y are dark brown and 

 greenish brown with very strong absorption, and for a brownish yellow. 

 Locally this brown hornblende is seen to grade over into a green variety. 

 The biotite also is dark brown. Like the former it is mainh' found 

 enclosed in the plagioclase, whose lamellae, of the albite twin type, in 

 sections J_ PM show x' : M =^8^, corresponding to Ab-.,, but many crystals 

 show a zonal structure, their central parts being more anorthitic. 



The plagioclase, especially the more albitic plagioclase which forms 

 the largest part of it, is present in the form of large xenomorphic individ- 

 uals which envelope all the other mineral grains. Of these the garnet, 

 pyroxene, apatite and rutile occur more in the form of independent crystals, 

 though very rounded and the pyroxene often ragged. The biotite and 

 hornblende and also the ilmenite are intimately associated with the plagio- 

 clase as small enclosed grains. 



Probably the garnet and pyroxene were the first minerals to crystal- 

 lize out in this rock, and it seems that the hornblende and plagioclase 

 were formed later at the expense of the former. This change apparently 

 took place at the last stage of consolidation. 



The evident resorption of the earliest minerals, however, was hardly 

 a phase of a normal process of crystallization, but rather due to changes 

 in the attendant physical conditions during that process. Or perhaps there 

 was a re-fusion of a true eclogite alread}- crystallized, and re-consolidation 

 of the hornblende-plagioclase mass now appearing as a mesostasis. 



We arrive at the conclusion that the eclogite-hornblende-gabbro of 

 Romsdalshorn contains two sets of minerals originated at different stages 

 of the rock development and under différent conditions. The earlier one 

 belongs to the eclogite facies while the later represents the typical horn- 

 blende-eabbro facies. 



Structural Types of Eclogite. 



The specimens on which the above quantitative inxestigations were 

 carried out were selected mainly as representatives of different structural 

 types. I did not then know, what was found later, on closer acquaintance, 

 that the chemical composition varies quite independently of the structure, 

 which is a function of the physical conditions during and, in part, after the 

 consolidation. It was much by accident that the examples studied never- 



