On the Formation of Pegmatite. 65 



cently by Klockmann, in the granitic pegmatite veins of 

 Kynast, of Schwarzbach, . etc., in Silesia (1. c. p. 399) ; 

 Klockmann himself, although otherwise agreeing with 

 Credner, has pointed out quite correctly that this structure 

 can hardly be brought into accord with Credner's theory, 

 In this connection it also deserves mention that Mr. H. 

 Backstrom and I have found perfectly pegmatitic large- 

 grained feldspar individuals forming the cores of spheres 

 occurring in centrically-formed massive granitite at Yasas- 

 taden near Stockholm. 1 



A further argument in favor of the magmatic solidifica- 

 tion of the pegmatite veins consists in the peculiarities of 

 structure which point towards a simultaneous crystalliza- 

 tion. First, the graphic structure which was more parti- 

 cularly referred to above, and which also occurs in a similar 

 way in massive eruptive rocks, must be mentioned. Further 

 also, must be considered the incomplete formation of the 

 pegmatite vein minerals which is generally evident when 

 these minerals have not crystallized out into drusy cavities 

 originally open (sometimes still so) ; this fact also was 

 more fully treated above. Such incomplete idiomorphicaily- 

 bounded crystals exhibit through their whole nature une- 

 quivocally, that they have crystallized out from a surround- 

 ing magma. 



As a peculiar detail of structure, which is also satisfac- 

 torily explained only upon the assumption of magmatic 

 solidification, may be mentioned the very frequent occur- 

 rence of bent, broken, and in part re-cemented cry.stalw; 

 examples have been described above in many places. 



As special structural forms, may be mentioned the some- 

 times exceptionally distinct fluid structures (Fluidalstruc- 

 turen) of the nepheline syenite pegmatite veins on the Lan- 

 gesund fjord. 



In assuming an eruptive origin for pegmatitic veins, 

 some have found great difficulty in the fact of the occasional 



1 See W. C. Briigger and II. Backstrfinr: " Om forekomsten af ' klotgranit', 

 i Vasastaden, Stockholm." (Jeol. Foren. FOrhandl. 1887, !>, 33] and 332, also Pig. 

 (5, p. 325. 



