On the Formation of Pegmatite. 41 



and this would exhibit symmetrical arrangement. The 

 filling-up is sometimes complete and sometimes only partial. 

 The preponderating feldspar is here siguificantly micro- 

 cline. Such a process might in many cases account for the 

 formation of the graphic granite and pegmatitic masses, 

 which form the mostly lenticular or vein-like accessory 

 component masses of granite rock." Rosenbusch expresses 

 himself very cautiously, so that it is rather difficult to 

 understand whether he proposes to consider the " gradual 

 secondary filling-up " as purely aqueous (hydatogenous), or 

 not. 



J. J. Harris Teall says of pegmatites: 'They occur 

 rather as segregations than as independent masses of erup- 

 tive origin." (British Petrography, p. 291.) 



Citations such as the above will suffice to show how, on 

 all sides, the difficulty of accounting for the pegmatitic 

 druses in the granite and for the larger occurences of peg- 

 matite in veins as formed by the same processes, has been felt. 

 If so much stress has generally been laid on the fact of small 

 pegmatitic druses and larger pegmatite vein-masses oc- 

 curring together in granite, and from this there has been 

 deduced a common interpretation of both as "simultaneous 

 segregations" (gleichzeitige Ausscheidungen) ; " separated 

 masses " (Aussonderungen) ; " segregation veins " (Aus- 

 scheidungstrumer), (cf. Primartrumer, Lossen), or as simi- 

 larly formed ".secondary fillings," etc., then this may per- 

 haps be essentially due to the fact that no correct conception 

 has been had of the extraordinarily frequent occurrence of 

 true pegmatite in the form of veins in rocks other than 

 granite. 



In my paper on the pegmatite veins at Moss I have men- 

 tioned how these veins, on the Annerod peninsula for ex- 

 ample, have a direction across that of the gneiss. Many of 

 these veins were followed for a distance of 200 to 250 

 metres, and were often 5 metres thick. The veins here 

 occur in gneiss, hornblende-schist and other crystalline 

 schists. Also along the coast between Langesund and 

 Christiansand, particula ly between Tvedestrand and Aren- 



