118 BÄCKSTRÖM, VESTANÅFÄLTET. 



the fine-grained granite, makes it highly probable, that the granulitic part of the »Dyne- 

 boda-gneiss» is also the common fine-grained granite, highly modified by rnechanical de- 

 formation. — The limits of the granulitic areas not being at present exactly known, these 

 areas on the accompanying map are marked as »gneiss with granite». 



The rocks of the quartzite belt. 



The quartzite belt in its lower, eastern part is composed of a pure quartzite, t hen 

 follows a mica schist, containing the conglomerate, then again quartzite and finally mica 

 schists rich in aluminous minerals. — The quartzite besides quartz contains only small 

 quantities of muscovite, hematite, rutile, zircon and still rarer apatite — the two last 

 mentioned with the form of trausported sand grains. Biotite has not been observed in any 

 of the rocks of the belt. — An analysis of this quartzite gave the following results; 



Si0 2 



AI2O3 Fe2(J 3 FeO MgO CaO Na 2 K2O H2O Sum. 



93,87 



1,59 1,68 0,67 0,20 0,70 0,27 0,53 0,76 100,27 



The hematite which it contains sometimes occurs concentrated into narrow bands, 

 upon one of which the old mine of Vestanå, well known for its minerals, was situated. 

 The iron ore, sometimes beautifully foldecl (Fig. 7), contains hematite, muscovite, cyanite, 

 and svanbergite, as shown under the microscope. 



95 per cent of the boulders of the conglomerate are grey quartzites, resembling the 

 quartzite beneath, the rest is vein quartz, quartzite rich in hematite and tourmaline-schists. 

 The grey quartzites sometimes show distinct bedding with dark lines along which iron 

 ore, rutile and rounded zircons are concentrated. — The rare boulders of tourmaline 

 schists vary greatly, ranging from rocks rich in tourmaline with small prismatic, or lar- 

 ger poikilitic cr\'stals of tourmaline, to luxullianites with spherulites of tourmaline in an 

 abundant groundmass of quartz. The tourmaline schists have not been found in place 

 but are considered to be derived from tourmaline-quartz-veins and from the impregnated 

 schists immediately surrounding such veins, produced by the pneumatolytic action of some 

 granite-eruption . 



The rocks occurring in the western half of the quartzite band are richer in musco- 

 vite and generally contain some of the special alumina minerals. These are here andalu- 

 site with manganandalusite, cyanite, ottrelite, and more seldom, fibrolite. The new vari- 

 ety »manganandalusite», recently described by the present writer, 1 has the physical properties 

 of common andalusite with the exception of a grassgreen colour and a strong pleochroisrn, 

 in which a = C and b = b are blue-green with a tinge of grass-green, c = a is more ab- 

 sorbed and shows an intense pwe yellow colour. The chemical composition of the speci- 

 men analyzed was: SiC>2 36,72, AI2O3 56,99, M112O3 6,91 = 100,62. 



In some parts of the district west and north of lake Bäen the alumina bearing 

 minerals, especially cyanite and ottrelite, are so richly present that distinct rock-types 

 »cyanite schists» and »ottrelite bearing cyanite schists» are produced. One of the latter, 

 from north west of Lake Bäen, showed the following chemical composition: 



1 Geologiska Föreningens Förhandlingar, Stockholm 1896, 18. p. 389. 



