Prof. F. Lceicinson-Lessing — Origin of the Igneous Rocks. 255 



closely connected with granites, forming a facies of these latter; the 

 alkaline syenites are connected with alkaline granites; the diorites 

 partly with the granites and partly with gabbros and norites. The 

 quartz-diorites are of course largely developed, bnt they are connected 

 petrographically and geologically with granites in such way that we 

 might speak of a granito-granodioritic formation as we speak of 

 a gabbro-pyroxenitic-peridotitic formation. The connexion between 

 the pyroxenites, the peridotites, and the anorthosites with the gabbro 

 formation has been already referred to. The gabbro-syenites 

 ( = monzonites) are equally derivates of the gabbro formation; such 

 rocks as adamellites, shonkinites, missourites, etc., are evidently also 

 facies of other regionally independent rocks. There remains one 

 rock-type whose position was not clear to me, and which seemed 

 to present a difficulty to my hypothesis of only two individual and 

 independent magmas, the granitic and the gabbro-noritic — I mean 

 the nepheline-syenites. But since Beljankin's ' researches in one of 

 the important regions, in the Ilmen Mountains of the Ural, have 

 demonstrated the connexion of the nepheline-syenite (miaskite) 

 formation with the granites, and Daly 2 has developed the view in 

 a recently published paper that all the nepheline-syenites are 

 derivates from granites, this last objection to my conception of only 

 two independent magmas is removed. 



As the effusives represent the same chemical types as the intrusives, 

 all that has been said before of the intrusive rocks is also applicable 

 to them. 



3. The original independence of the gi'anitic (including the 

 granodioritic) and of the gabbro-pyroxenitic-peridotitic formations 

 is further corroborated by the fact that they are generally more 

 or less differentiated and rich in facies and in diaschistic veins and 

 dykes. The differentiation of these formations is quite natural if 

 they are considered as original primordial magmas, as well as the 

 absence or small degree of differentiation that is characteristic of 

 such rocks as syenite, diorite, and monzonite, which are themselves 

 differentiation products. 



4. Another fact corroborating the original independence of the 

 granitic and the gabbro-noritic formations is the absence of such 

 transitional types as would speak for the production of one of 

 them from the other through differentiation. Amongst regions well 

 known to me personally, I can cite the Caucasus and the Ural 

 Mountains, where these two formations are nearly equally developed 

 and quite independent of one another, and where I have not found 

 transitional types between the two formations in question. On 

 the other hand we know from the studies of Harker 3 that where the 

 granitic magma is mixed with gabbro there are formed such 



1 D. Beljankin, " Petrographical Sketches of the Ilmen Mounts," ii : Ann. 

 Inst. Polyt. St. Petersbourg, vol. xiii, p. 715, 1910. 



2 E. Daly, " Origin of the Alkaline Eocks " : Bull. Geol. Soc. Amer., vol. xxi, 

 p. 87, 1910. 



3 A. Harker, The Natural History of Igneous RocTcs, 1909. Amongst 

 different papers of the author cited in this work see especially ' ' The Tertiary 

 Igneous Eocks of Skye " (Mem. Geol. Surv., 1904). 



