64 Canadian Record of Science. 



which differ from these in composition; in a special part 

 of this Treatise, under akmite, the relationship between 

 the fine-grained apophyses of the aegerine granite district 

 and the akmite pegmatite vein of Rundemyr, is pointed 

 out. 



To every one who has occupied himself with a thorough 

 study of the methods of formation of pegmatitic veins and 

 lias had opportunity of investigating in the case of hundreds 

 and hundreds of veins of all varieties of occurrence, their 

 close approximation to the normal eruptive vein type and 

 their very various transitions to and connections with the 

 same, these purely geognostic peculiarities of occurrence 

 will perhaps be considered as the strongest proof of the un- 

 doubted eruptive origin of the veins. 



3. The varieties of structure of pegmatite rocks are of 

 kinds which in part at least are known only in eruptive 

 rocks. In the case of acid granitic pegmatite veins there is 

 very often a purely eugranitic granular structure with 

 coarse grain (e. g. in the granitite of numberless pegmatite 

 veins near Stockholm) ; in the nepheliue syenite pegmatite 

 veins, as has been mentioned above, a coarse-grained typical 

 trachytoidal structure, corresponding to the foya'ites of the 

 Laugenthal (g. g. Laven), is frequently observed. The drusy 

 structure of many pegmatite veins, particularly of granitic 

 ones, is not (as considered e. g. by Klockmann 1. c. p. 40^) 

 an argument against the eruptive nature of pegmatite, but 

 is frequently very characteristically developed as large 

 laccolites in the boundary zones of granitic rocks themselves 

 (e. g. Hortekollen, Solbergfjeld, near Drammen, Norway, 

 Holmsboe and Eodtangen on the Drammenfjord, etc.). The 

 peculiarity of structure most convincing in its nature, 

 which must be considered virtually as proof of the eruptive 

 formation and magmatic solidification of pegmatite veins in 

 general, is the centric structure (spheroidal structure) first 

 described by L. v Buch, afterwards by G. Rose, and re- 



the mc-e massive granites recognized as eruptive. An unprejudiced observer 

 will not wish to make such a separation," <fcc J. H. L. Vogt 'Kristiania Vid. 

 Selsk. Forhandl. 1881, No. 9. p. 28), describes, occurring at Skarningsfos, a gran- 

 ite pegmatite apophysis in gneiss, Sec, passing directly into the main granitite. 



