J. V. Elsden — Origin of Pegmatite Veins. 309 



them to the infilling of cracks and fissures formed subsequently to 

 the consolidation of the parent rock. Charpentier, in his examination 

 of the Pyrenees in 1823, conceived the view that pegmatites are 

 true fissure veins, injected by portions of the still fluid part of the 

 magma from below. This view has been largely adopted by the 

 French geologists, and also by De La Beche in this country, and by 

 Naumann, Giimbel, and others in Germany. Such veins would 

 seem to form the " Injectionsschlieren " of Eeyer,^ and are similar 

 to what are sometimes termed contemporaneous veins. De Saussure, 

 G. vom Rath, and others, however, maintained that these veins were 

 deposits from watei-y solutions; while Forchhammer, Sandberger, 

 and Credner advocated the theory of lateral secretion, involving the 

 assumption that pegmatite veins are true fissures filled up with 

 minerals leached out from the surrounding rock. Eosenbusch^ 

 associates pegmatite veins with drusy and miarolitic structures, or 

 vein-like cavities filled up by secondary crystallisation, a view also 

 briefly suggested by Teall.^ Later observers have modified these 

 theories with a view to the explanation of the marked acidity of 

 pegmatite veins in comparison with that of the parent rock. Thus 

 Brogger, in his well-known work on the rocks of the Christiania 

 district,* found evidence to show that these veins represent true 

 eruptive outpourings, the last aufpressimgen of a differentiated magma 

 basin. This view somewhat corresponds to the hjsterogenetische 

 scMieren of Eeyer, or the ausscheidimgstrilmmer referred to by 

 Kalkowsky* in his description of the pegmatites in the granulite 

 of Saxony. Later observations of Messrs. Gunn, Hinxman, Barrow, 

 Kynaston, Clough, Cunningham-Craig, and Wilson, in the Highlands 

 of Scotland,^ have led in the majority of cases to the conclusion that 

 the pegmatite veins are subsequent intrusions, although in a few 

 cases they are referred to as of segregative origin ; but whether 

 these segregations were of a magmatic type or merely the results of 

 subsequent metamorphism is not always clearly indicated. Keilhau, 

 writing in 1838 on the Christiania pegmatites, attributed them to 

 simultaneous separations of the surrounding eruptive mass, and not 

 to the filling up of fissures ; but no one, so far as I am aware, has 

 described evidence of the original existence of such veins in the 

 form of acid streaks in a viscous magma, prior to consolidation. 



The remarkable agreement in the characters of pegmatite veins in 

 widely separated areas points to some general law governing their 

 mode of origin. It is, therefore, somewhat strange that the views 

 advanced concerning their formation should still remain so much at 

 variance. It seems at least certain that the pegmatites of Blekinge 

 province, in Sweden, present peculiarities which absolutely preclude 

 the suggestion that these are subsequent fissure injections of the 



1 See Zirkel, "Lehrbuch der Petrographie," vol. i, p. 787 et seq. 



* Mikroskopische Physiographie d. Mass. Gesteine, ii, p. 39. 

 3 " British Petrography," p. 291. 



* " Die Mineralien der Syenit pegmatitgauge," etc., Leipzig, 1890. 



5 Zeit. d. d. geol. Ges., vol. xxxiii (1881), p. 653. 



6 See " Summary of Progress," 1899, 1900, 1901, 1902. 



