758 H. A. BROUWER 



sonite is a rare constituent of the rocks from the Pilandsberg, while 

 true arfvedsonite lujaurites have been described by Ussing from 

 Greenland. The lujaurites are connected with the foyaites by 

 rock types poorer in dark minerals, aegirine with the needle form 

 gradually disappearing. Like the lujaurites from other regions 

 (Greenland, Kola peninsula, and Los islands), the rocks of the 

 Transvaal are characterized by an abundance of rare minerals. 

 For example, the new mineral molengraafhte, 1 of the eucolite 

 group, which sometimes occurs in the foyaites, is very common in 

 these lujaurites. 



At both sides of the Rustenburg road, on Ledig [744], we find 

 tinguaitic rocks and porphyritic lujaurites between the high 

 lujaurite hills and the norites; to the east the lujaurites can be 

 followed to Doornhoek [134]. Their southern parts are covered 

 by effusive rocks. To the northwest, bending round with the 

 periphery of the Pilandsberg, we can follow the lujaurites to the 

 southwestern part of Wijdhoek [701]; farther to the northwest 

 the periphery of the complex is formed by red to light-red syenitic 

 rocks. On Tusschenkomst [331] we find the same lujaurites in 

 contact with the effusive rocks, where a valley separates ridges of 

 the two rocks. 



The tops of the eroded lujaurite ridges are similar to those of 

 inclined crystalline schists. 



We find the lujaurites and their porphyritic equivalents also 

 in the western, northern, and northeastern part of the complex, 

 beside the red syenites; in the eastern part, where the effusive 

 rocks have their greatest development, the latter rocks cover the 

 whole surface from the periphery to the central foyaites. Probably 

 the lujaurites occur there at greater depth. The nepheline syenites 

 and the allied rocks which hitherto have been studied micro- 

 scopically belong to the following groups: 



1. Aegirine foyaites 

 Leucocratic rocks 

 Mesocratic rocks 

 Foyaitic lujaurites 



1 H. A. Brouwer, " Molengraaffit, ein neues Mineral in Lujauriten aus Transvaal," 

 Centralbl. f. Min., etc., 19 11, p. 129. 



