158 GREAT SERPENTINE BELT OF NEW SOUTH WALES, iv., 



terobase (minverite) in which the albite is chiefly primary, 

 though a small amount of albite basic felspar may be recognised. 

 The quartz-diabases in the same series are not albitised at all. 

 By the escape of the sodic solutions from the igneous rock into 

 the surrounding mudstones, adinoles are produced. The occur- 

 rence of the minverites shows that albite may crystallise directly 

 from a differentiate of the spilitic magma, although, in the 

 British rocks, according to this view, it was usually segregated 

 into post-volcanic solutions that attacked and replaced the 

 originally crystallised basic felspar. Bowen(22) and others de- 

 scribe the development of albitic facies in the upper portions of 

 doleritic masses, and the escape of the albite into the overlying 

 sediments, producing adinole. Bowen believes that the albitic 

 rocks are the result of the intrusion of gabbroid magma into 

 argillites, and that the water contained in the sediments has 

 taken part in the transfer of the albite-molecule out of the normal 

 magma. Daly supports this view, believing that the examination 

 of sills, from the top to the bottom, will show an upward enrich- 

 ment in albite. " The submarine origin of the pillow-lavas 

 implies that the magma passed through wet sediments of greater 

 or less thickness. Under these conditions, water-gas must play 

 an important role in modifying the magma in the vents, and it 

 seems impossible to doubt that, occasionally, the upper part of 

 the magma-column, and also some of the extruded lava, will 

 become albitised. Meanwhile, the general body of the igneous 

 rock must often be profoundly altered by the absorbed water-gas 

 or hot water, exactly as described by many authors writing of 



the spilitic masses The writer believes that the spilite 



rocks are pneumatolytic derivatives of normal basaltic magmas, 

 and that the modifying gas is chiefly water of resurgent, not of 

 juvenile origin. "(9, p. 340). 



The spilitic rocks of the Nundle district differ from the 

 majority of those discussed by Messrs. Flett, Dewey, and Daly, 

 in the almost complete absence of signs of secondary origin of 

 the felspar, and the rocks as a whole are fresh. Clear albite 

 prisms may occur in ophitic intergrowth with undecomposed 

 pyroxene, a thing difficult to explain on the hypothesis of the 



