02 ■ PF.NTTI FSKOI.A. M.-N. Kl. 



eclogites, ns is a cominoii case in many lands, generali}' cr)nsist of rocks 

 that may be petrographically characterized as amphibolites or diorites or 

 hornblende-gabbros. Their mineral composition almost without exception 

 conforms to the ampliibolitc faciès. 



Now, it is possible that, in many cases, such inclusions have once 

 consisted of eclogites, while in other cases such a supposition would have 

 no reason. In any case, all siu h inckisions, eclogitic as well as amphibolitic, 

 are analogous in being "basic" aggregates of gabbroid composition enclosed 

 in granitic rocks. 



One would therefore suspect a close genetic connection, a consanguinity, 

 between the inclusions and their country-rock and, in some cases, this is 

 very obvious in fact. Such is the case in the so-called anticlinal batholiths ' 

 in the Fcnno-Scandian Archaean, to which belongs the Orijärvi granite 

 studied by the present writer. v\s I have set forth ^, the dark inclusions 

 are probably fragments fi-om the gabbro-dioritic portions of the batholiths 

 consolidated earliest as the boundary -zones of the mass. 



In the present case this theory, however, can hardly be applied in 

 such a simple form. It is not possible to state with certainty the mechanism 

 of intrusions and differentiation of such gneiss-masses as that of Nordfjord 

 and More. But one is sure that fluctuations on a large scale, caused by 

 the effective stress, have taken place in the crystallizing and differentiating 

 gneiss magma. Although a consanguinity relation is probable and the 

 process of differentiation of the gneiss, as a whole, may have been owing 

 to the gravitative control in the manner emphasized by R. A. Daly^, there 

 may have been chances for the inclusions to be caught up from beneath 

 as well as to sink down from above. 



The question now arises, whether die inclusions have consolidated 

 within the gneiss magma, as must be assumed in the case of the eclogite 

 in the olivine-rock, or have been detached from larger consolidated eclogite- 

 masses. Unfortunately the field evidence, on this point, is not quite con- 

 clusive. If the inclusions were concretions, or aggregations of crystals 

 separated out from the magma, they should show concentric structures. 

 Some kind of concentricity may actually be noted in smaller fragments, 

 appearing in a concentric foliation, or in the enrichment in tht salic con- 

 stituents of the amphibolitized border zones, but these are probably all due 

 to later influences, as is the amphibolitization itself. Most of the small 

 lenses, in their unaltered portions, are quite non-foliated. 



Band-structure is very common in the inclusions, being always parallel 

 to Uieir elongation. I never observed that the bandine- would conform to 



' Per Geijer, On the Intrusion Mechanism of the Archaean Granites of Central Sweden. 



Bull. Gool. Inst. University of Upsala, XV, p. 47, 1916. 

 2 Pentti Eskola, On the Petrology of the Orijärvi Region. Bull. Comm. geol. Fini. 40, 



1914, p. 64. 

 ^ R. A. Daly, Igneous Rocks and their Origin. 1913. 



