126 BÄCKSTRÖM, VESTANÄFÄLTET. 



metamorphism had acted very quietly, only transforming in situ. But future investiga- 

 tions may perhaps prpve,, that these felspar-accumulations are only structural phenomena 

 characteristic of an intense contact-metamorphism, which may be produced even in a 

 quite homogeneous material, rieh in felspar. 



In the stronger pressed gneisses quartz and mica are crushed and form fine-grained 

 zones, surrounding the larger and still isometric felspars. Often felspar accumulations 

 with well preserved polygonal structure are observed in these crushed gneisses. 



Of the gneisses in the northern continuation of the Vestanå region one — the 

 »Örsjö»-gneiss — is a red, fine-grained gneiss, poor in dark minerals and with irregular 

 allotriomorphic structure; its origin is undetermined. — Another, the »Halen»-gneiss, has 

 structural and rnineralogical elements from the »Gillesnäs»-gneisses as well as from the 

 granites. It needs further study. — A third, occurring in the region north of the map, 

 is a medium or coärse-grained, generally crushed gneiss with the mineral composition of 

 a hornblende-bearing, somewhat more basic gneiss of the previously described type. Its 

 primary structure is that due to an intense contact-metamorphism. 



The gneisses west of the quartzite belt. 



The gneiss, occurring on the western, hanging, side of the quartzite belt was for- 

 merly considered to belong to the great »magnetite-gneiss» region of western Sweden. In- 

 vestigation shows, that the »magnetite-gneiss» between the quartzite belt and Lake Immeln 

 is composed of two different rocks, one a dynamo-metarnorphosed granite (see p. 117) the 

 other a gneiss of sedimentary origin. The latter is generally strongly dynamo-metarnor- 

 phosed, but its primary structure, when recognizable, is a contact structure. Large skeleton 

 muscovites or poikilitic hornblendes occur, and also poikilitic felspars (Fig. 34), as well 

 as typical »felspar-accumulations» of the kind described. The mineral composition appears 

 to be the same as the somewhat pressed fine-grained gneisses east of the quartzite belt 

 and it also agrees quantitatively, as far as may be judged from microscopical examination 

 alone. It therefore appears probable, that the gneisses on both sides of the quartzite- 

 amphibolite belt belong to one single formation, that on both sides is older than the 

 quartzite and separated from it by the great amphibolite bed, and into which the quartzite- 

 amphibolite-complex has been folded. This view is supported by the fact, that when the 

 quartzite belt to the north-west tapers out and disappears, the eastern and western gneisses 

 meet Avithout boundary. 



The »granite-gneiss». 



The south-western and southern part of the area shown on the map is occupied by 

 a »granite-gneiss». On the island Ifön and the region east of Lake Ifösjön the rock is quite 

 massive and granitic, but passes north of Ifösjön into a schistose »eyed granite», strongly 

 crushed like all the other rocks in this part of the district. It differs mineralogically 



