GEOLOGY 365 



conditions of magmatic differentiation necessary for the pro- 

 duction of alkaline types are more often realised in regions of 

 this structural character than in folding zones. 



In continuation of former work R. Brauns has now pub- 

 lished a thorough investigation of the phonolitic rocks of the 

 Laach region (Eifel) [Neues Jahrbuch f. Min. Beil.-Band., 

 16, 1922, pp. 1-116). This area includes the well-known 

 leucitophyre of the Rieden, which appears under the unfamiliar 

 name of selbergite, on the ground that it is really a dyke rock, 

 not a lava, to which form the term leucitophyre is correctly 

 applied. Selbergite is therefore nosean-leucite-tinguaite-por- 

 phyry ; schorenbergite, similarly, is a new name given to a 

 nosean-tinguaite-porphyry. The mineralogical and textural 

 differences between these rocks and the corresponding effusive 

 forms seem scarcely worth the bestowal of new names. Numer- 

 ous inclusions of plutonic rocks of alkaline character occur as 

 fragments in the tuff vents of the Eifel. Among them are 

 nepheline-syenite, nosean-syenite, and cancrinite-syenite, as 

 well as calcite-syenite, in which the carbonate is regarded as a 

 primary pyrogenetic mineral. Riedenite is a new name given 

 to a nosean-biotite-pyroxene-rock occurring in this way. Its 

 chemical affinities appear to be with theralite and shonkinite. 



Prof. S. J. Shand has described the geological and petro- 

 logical relations of the small syenitic mass of Leeuwfontein, 

 Pretoria district {Trans. Geol. Soc. S.Africa, 24, 192 1 , pp. 232-49). 

 It forms an elliptical outcrop occupying 2| square miles, and 

 the igneous complex is intruded into quartzites of the Pretoria 

 Series. The mass represents the differentiated rocks of an old 

 volcanic vent. Soda-trachyte was first erupted ; and this 

 rock was successively broken by confocal plugs of white syenite 

 (akerite), red syenite (umptekite), and nepheline-syenite. This 

 vent is practically in line with at least three others of similar 

 characters, forming a series akin to that of the Monteregian 

 Hills, near Montreal. A welcome feature of the petrographical 

 part of the paper is the suggested extinction of four unnecessary 

 rock names, viz. leeuwfonteinite, hatherlite, pilandite, and 

 pienaarite, which have been applied to various phases of this 

 complex. 



An important petrographical memoir by D. Rotman has 

 belatedly come to hand from Roumania (" Das Eruptivmassiv 

 von Greci, District Tulf:ea, Dobrogea, Petrog. Studie," Anuar. 

 Inst. Geol. Romdniei, 7, (191 3), Bugarest, 191 7, pp. 249-425). 

 It is an intensive study of a typical Cordilleran magma, injected 

 into the Devonian and Permo-Carboniferous sediments of the 

 Dobrogea fold mountains. Two series of rocks are distinguished : 

 an amphibole-granite — granodiorite — tonalite series ; and a 

 mica-poor granite — gabbro series. These are regarded as the 



