98 F. LOEWINSON-LESSING 



Hastings region, that the zones of contact coincide with the cleav- 

 age surfaces of the gneisses, Hmestones, and other rocks, and since 

 the cleavage is parallel to the stratification planes, the meta- 

 morphic zones argue for the laccolithic and not batholithic char- 

 acter of these bodies. Bowen's mention of the local occurrence of 

 perthitic feldspar is hardly an argument for the hypothesis that 

 the anorthosite was covered by syenite, that both are derived from 

 a basaltic magma, and that the anorthosite is a sheetlike mass, 

 like the intrusive mass of the Adirondacks. Of course, in stating 

 that the Adirondak massive is a sheetlike body consisting of anortho- 

 site at the bottom and syenite at the top (both rocks resulting from 

 a differentiation in situ of a basaltic mother-magma), Bowen is 

 cautious and considers this interpretation a conditional one: "And 

 again, the writer's interpretation of the igneous mass as sheetlike 

 is offered merely because of the difficulties of picturing the general 

 relation otherwise."^ At the same time he mentions xenohths of 

 Grenville rock in the anorthosite, a feature suggesting the intrusive 

 character of the anorthosites, and gives examples of assimilation 

 of the covering rock by the syenite, etc. All these data show that 

 the stratigraphical features are not conclusive for Bowen's views. 

 And furthermore, it is rather doubtful whether the accumulation 

 of labradorite crystals at the bottom and the separation of a syenitic 

 liquid at the top do agree with their respective densities at the tem- 

 peratures existing during the stage of crystalhzation when this 

 differentiation was going on. 



The connection of anorthosite with syenites in the Morin and 

 Andirondack bodies is conspicuous, but their genetic relations are 

 not sufiiciently evident. Gushing considers the Adirondack syenite 

 as 3'^ounger than the anorthosite, the syenite sending apophyses into 

 the anorthosite — a statement decidedly invalidating Bowen's 

 interpretations. 



The other labradorite regions do not afford such stratigraphical 

 data as could be made use of for sustaining this or that interpreta- 

 tion. I could find such data neither in Kolderup's^ writings on the 



' N. L. Bowen, "The Problem of the Anorthosites," /oz»-. Geol., Vol. XXV (1917), 

 p. 226. 



^ K. Kolderup, "Die Labradorfelse des westlichen Nonvegens. la, II," Bcrgens 

 Mus. Aarbog, Vol. I (1896; Vol. V (1903), No. 12. 



