I92I.X0. 8. 0.\ THE ECLOGUES OK NORWAY. 61 



as lenses of eclogite and in the other case as schhers and bands rich 

 in hornblende, is genetically one and the same thing-. 



P^rom the occurrence of the eclogite as lenticular inclusions in the 

 igneous gneiss it follows, that they must have consolidated earlier than 

 the gneiss. A remarkable exception to this rule, however, was met with 

 on Seljenaes, near the occurrence o( margarite-bearing orbicular labradorite- 

 rock described later on. 



About 100 meters south of Seljenaesholmen there is, on the low shore 

 plain, an occurrence of eclogite bounded directly bv augengneiss. The 

 eclogite contains some rounded fragments of the latter. The gneiss has 

 hereby been altered in the most peculiar way: Small fragments have been 

 changed entirely into a mass of mica, for the most part muscovite. The 

 same is the case with the central zones of the larger fragments, but to- 

 wards the centre the latter pass gradually over into a rock in which some 

 feldspar and, in the very largest, a litde of the eye-structure ma}' still be 

 seen. In the eclogite, on the other hand, there is a narrow "endogenous" 

 contact-zone, in which the rock has been amphibolitized. \n some cases 

 the boundary-zone is rich in garnet. 



This occurrence may be interpreted in one way onlv: Fragments of 

 the eyed gneiss, already consolidated, had been detached from the large 

 mass by the eclogite magma and been enclosed in it. The temperature of 

 the latter, however, vv-as high enough to cause the refusion- of the quartz- 

 leldspar (eutecticum?) of the gneiss; this molten mass was squeezed out 

 and the mica alone remained and was clustered into a compact mass. 



Exceedingh' interesting as the phenomenon is, it is, however, an ex- 

 ception. Hundreds of other occurrences of eclogite are obvious inclusions 

 in the gneiss, and there is no way open to explain them as intrusions, 

 nor is it possible to apply the explanation used by J. j. Sederholm ' in 

 assuming primarih' basaltic dikes, when their countrv-rock had been re- 

 fused, to have been converted into series of inclusions of amphibolite. As 

 a rule, the lenses are true inclusions in the gneiss. 



• The importance of the Seljenaes occurrence lies in its e\-idence that 

 an opposite case also was physically possible: that once, in connection 

 with the great orogenetic movements, a solid gneiss mass was pressed 

 down deep enough to meet gabbroid magma which, after having enclosed 

 fragments from the gneiss, solidified as a true eclogite. 



T/ir i/ic/z/sioi/s of Eclogite couipaird i\.<ith other "dark Iiicliisioiis" 



iti Gneiss or Granite. 

 The inclusions of eclogite, in the gneiss of More and Nordtjord, play 

 the same rôle as the so-called basic or "dark" inclusions in many other 

 masses of granites and gneisses. The last-named inclusions, il thev are not 



' J. J. Sederholm, Om Granit och Gneis. Bull. Com. géol. Fini. 23. 1907. 



