1921. No. 8. ON THE ECLOGITES OF NORWAY. 57 



segregations from the kimberlite magma. As a chief argument in favoui- 

 of the former opinion the fact has been set fortli, that these nodules, in 

 their mineral composition, are perfectly similar to the true eclogites which, 

 though with insufficient evidence, have been regarded as being of meta- 

 morphic origin, while the assumption of segregations from the kimberlite 

 magma should postulate a primary crystallization h-om the magma. This 

 argument loses its force, as we now find, in the Norwegian rocks, examples 

 of "true eclogites" that are of primary igneous origin. 



As another proof for his belief that the nodules are not genetically 

 connected with the eclogites, F. P. Mennell ^ sets forth the difference in the 

 composition of the garnets in the nodules and in the kimberlite, the former 

 being richer in almandite. According to the analyses quoted by Mennell 

 two eclogite-garnets from Colossus Mine, Rhodesia, have the compositions 

 Feg^MgggCagj, and Fe^^Mg^gCa.^.^ respectively, while one of the garnet from 

 the kimberlite leads to the formula Fci^Mgv.X'a^i. hi reference to this we 

 may remark, that a similar difference also obtains between the garnet in 

 the eclogitic nodules and bands (Fe.,7Mg,;j^Caj^2) and in their dunitic countr\'- 

 rock (Fe.jgMgggCaio) from Sondmore. 



The perfect analog}' with the masses of eclogite in our dunite also 

 strenghtens the conclusion that the nodules of eclogite in the kimberlite 

 are genetically connected with their country-rock, though not necessarily 

 segregations of earlier date. Other evidences are: the extensive distribution 

 and persistent characters of the nodules in the kimberlite pipes in South 

 Africa, and also in N. S. Wales-, the non-occurrence of other kinds of 

 eclogite in the same region-^ and, above all, the occurrence of diamond in 

 the nodules, even enclosed in the garnet. These evidences would seem to 

 be conclusive in themselves. 



In summarv, the band-shaped masses of eclogite etc. in the 

 o 1 i \' i n e-i" o c k in S n d m o r e are crystallizations o 1" igneous 

 character connected with the country-rock and probably of 

 a somewhat later date. Analogous masses of eclogite have 

 been found in ol i \- i n e-rocks of other regions and in the 

 k i m b e r 1 i t e s of the d i a m o n d-b earing pipes. 



' F. P. Mennell, The Geological Structure of Southern Rhodesia. Quart. Journ. Geol. See. 

 66, 1910, p. 353. 



2 (ieorge W. Card, An Eclogite-bcaring Breccia from the Bingera Diamond Field, Rec. ot 

 the Geol. .Surv. of N. S. Wales, 7, 1902, 29 — 39. 



3 F. P. Mennell (loc. cit.) mentions that eclogite should occur in pre-Cambrian schists around 

 granite massifs. As, however, no characteristics are given, it is not sure that a true 

 eclogite, and not e. g. garnet-amphibolite or diopside-grossularite is in question. 



