122 BÄCKSTRÖM, VESTANÅFÄLTET. 



into the eommon grey gneiss, occurring över the eastern part of the distriet and conti- 

 nuing över a great part of Blekinge. The passage is quite continuous, in the field as 

 well under the microscope. The gneiss is older than the numerous granites of the distriet 

 and all varieties carry the mark of contact-metamorphism in their strueture. With the 

 exception of the part next to the quartzite band they are all highly metamorphosed and 

 quite gneissic, and of that upper part those portions near the granite contact are also 

 gneissic. It therefore appears probable, that the dense fine-grained gneiss represents the 

 less metamorphosed and uppermost parts of a widely extended gneiss formation, which is 

 very nearly homogenous both in material and in age. In the upper parts the contact- 

 metamorphism was more local, but a,t greater distances from the sm"face the different 

 contact zones of the granites overlapped another, producing a metamorphism of more 

 regional character. 



The following analyses show the comparatively great homogeneousness of the mate- 

 rial of the gneisses from different parts of the distriet and at the same tiine its cheinical 

 character : 



1. 

 S1O2 70,46 



AbA - 13,24 



FeA ----- - - - - l,9i 



FeÖ 2,58 



MnO 0,56 



MgO_... 0,78 



CaO 4,33 



Na 2 l,3i 



K 2 6 3,59 



Ii, O 1,27 



TiOa — 



100,03 99,77 99,78 



] . Dense fine-grained gneiss from NNE of south end of Lake Raslången, 2. Gneiss 

 from the shore of Lake Raslången, E. of Kidön, 4 meters from the granite contact, 3. 

 Gneiss from 'Pukavik on the Baltic Sea. 



The gneisses consequently have the chemical composition of rocks of the quartz- 

 diorite family, the variations from it in the first example being those that an original 

 weathering of the material would produce. ■ — But the gneisses contain conformable layers of 

 of mica schists (se map, plate 1), Avhich, as will be shown låter on, must be of sedimen- 

 tary origin; consequently, the material composing the gneisses must also have been a sedi- 

 ment. This sediment, having the composition of a comparatively chemically unaltered 

 rock of the quartz-diorite family, must have resulted from an essentially mechanical de- 

 struetion of such a dioritic rock, and must therefore be an arkose or a tuff. Now many 

 of the dense fine-grained gneisses and gneisses of the distriet contain large quartz grams! 

 These are generall}- irregularly shaped, but in the least altered dense fine-grained gneisses 

 their original form bas been preserved and shows itself to be the dihexahedral form 



2. 



9 



67,99 



68,43 



14,04 



16,05 



1,71 



1,73 



3,04 



1,02 



0,39 



0,35 



1,00 



0,91 



4,11 



3,66 



2,73 



3,04 



3,99 



3,70 



0,77 



0,46 



Trace 



0,43 



