KONGL. .SV. VKT. AKAMvMIKNS II A \ I H.l N< i A K. I i \ M 



29. n:o 4. I 



Another proof of the sedimentation of the material by water is found in a dark 

 varietj From wesl of Kroksjön. Thia rock is exceptionally rich in the dark and heavy 



minerals, consisting of biotdte, inni ore and apati te besides quartz and s felspar. The 



beavy minerals are arranged in strings, in vvhich the waterworn and rounded, sometimes 

 broken apatite-prisms lie parallel to the bedding. — In auother of the intercalated schists 

 a fragmenl of a rock consisting of garnel and quartz was found, showing, thal in these 

 schists there also oceurs material, foreign to the more or less weathered tuff. 



The intercalated schists rich in quartz and muscovite do not occur in the lower 

 paris of the gneiss series, linl increase in number upwards, thus forraing a connection 

 between the tuff material and the overlying sand and clay formation. Appafently there 

 < • ■■ 1 1 1 1 h > i be ■• 1 1 1 \ great difference of age between the quartzite .formation and the gneiss. 



The highly metamorphosed gneisses of the Pukavik - and dllesnäs -type. 



Of the highly metamorphosed gneisses, belongiug to the same series as the former, 

 some few examples may be given. 



The gneiss from Pukavik on the Baltic Sea, whose analysis has been previously 

 given (p. 122), contains about 28 per cent of quartz, 44 of andesine (Ab 3 An 2 ), 19 of 

 orthoclase and microeline, 7 of biotite and 3 of iron ore, apatite, zircon and titanite. 

 The biotite oceurs as small formless scales. The average size of grain of the quartz and 

 felspars is about 0,4 mm. The rock is very fresh and shows little effects of pressure. 

 Its strueture, illustrated by Fig. 30, may be said to be a somewhat modified hornstone- 

 strueture. The quartz and felspar grains are never idiomorphic but isometric and more 

 or less polygonal. 



Another example from SSW of N. Gillesnäs, Jemshög parish, is hornblende-bearing. 

 The hornblende, as shown by Fig. 27, oceurs as large poikilitic individuals, and the accom- 

 panying biotite is in small formless scales. As for the white minerals the same may be 

 said as in the gneiss from Pukavik, that the strueture is that of a hornstone with iso- 

 metric polygonal grains of quartz and felspars. But in regard to quartz and microeline 

 there are differences from the normal hornstone strueture, since their form is not so re- 

 gularly polygonal and not so isometric as that of the plagioclase. This miglit be consi- 

 dered a first step towards the hypidiomorphic strueture of the abyssal igneous rocks, but, 

 as anomalies of this kind are still more developed in the corresponcling gneisses, which 

 are less fresh and a little more pressed, the differences may be interpreted in the same 

 way as the similar differences from the normal strueture of the granites of the district, 

 namely as produced by the låter tectonic movements seconded by commencing metasomatic 

 processes. 



Felspar accumulations, composed of andesine or microeline in polygonal grains, occur 

 in many of the highly metamorphosed gneisses. As they may be followed back to the 

 felspar spöts of the dense fine-grained gneisses, it is possible, that like them they represent 

 the former felspar-phenoerysts of the tuff, and they would then indicate, that contact- 



