488 F. Diwey—The Magnesian Group of Igneous Rocks. 
Finally, it should be noticed that effusive rocks corresponding to 
the older and more important members of the group, such as the 
Charnockite Series and associated rocks, are not known, and also 
that the rocks of most of the magnesian provinces have been invaded 
by intrusions of very different composition, namely nepheline- 
syenites and associated rocks belonging to the Alkaline Series ; 
as examples of these last may be given the nepheline-syenites of the 
Los Islands (West Africa),! the nepheline-syenites of India,? and 
the alkaline rocks of Scandinavia.® 
The present writer recognizes that the Magnesian Group of rocks 
is not sharply divided from the rocks relatively poor in magnesium, 
any more than the alkaline, calc-alkaline, spilitic, and other petro- 
graphic suites are sharply divided from each other; most of these 
suites, in fact, either overlap or are indistinguishable at their acid 
and basic ends respectively, and it is, moreover, not always possible 
to distinguish between their intermediate members. Nevertheless, 
the conception of these suites has so far served a very useful purpose 
in petrography. 
III. Tar MacGnestan PROVINCES. 
Reference has already been made to two examples of Magnesian 
Provinces, but there is reason to believe that similar Provinces exist 
also in the ten additional areas listed below ; the rocks of the Group, 
however, appear to be developed to a variable extent in the different 
Provinces, and subsequent investigation may necessitate modification 
or extension of the list. 
1. Ekersund, Soggendal, and Bergen districts in western and 
south-western Norway.* 
2. Saxony and neighbouring areas, from which “ pyroxene- 
granulites”’ and “ pyroxene-gneisses”’ have frequently 
been described by earlier writers.” 
Ural Mountains.° (The rocks of this area, although 
resembling those of the other areas in many respects, 
generally Geary augite instead of hypersthene.) 
4. Southern India.’ 
5. West Africa.° 
6. Hastern part of Ellesmere Land and Prudhoe Land.’ 
1 Lacroix, op. cit., 1911. 
2 Mem. Geol. Surv. India, vol. xxx, 1900, pt. ii. 
Daly has commented upon the association of anorthositic and syenitic 
types both in the Adirondacks and in Western Norway. See Igneous Rocks 
and their Origin, 1914, p. 54. 
4 C. F. Kolderun, Berg. Mus. Aarb., 1896, No. V; also 1903, No. 12. 
> Rosenbusch, Hlemente der Glestetnslehre, 1910, p. 187. 
6 See H. S. Washington, ‘‘ The Charnackite Series of Igneous Rocks” : 
Amer. Journ. Sct., 1916, p. 323. Also J. P. Iddings, Igneous Rocks, vol. ii, 
1913, p. 511. 
7 Memoirs Geol. Surv. India. 
8 See above, p. 486. 
°C. Bugge, Rep. 2nd Fram Exped., No. 22, 1910. 
(Se) 
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