582 THE DISTRIBUTION, KTC., OF ALKALINE ROCKS, 



taken place. Undoubtedly his contention is correct. We can, 

 nevertheless, imagine assimilation to have proceeded in a more 

 deep-seated reservoir, and differentiation to have taken place in 

 the various bathylitic masses ejected from the reservoir, and we 

 can fall back upon the evidence afforded by Daley's Okanagan 

 bathyliths, by Bayley's eruptive rocks of Pigeon Point, by 

 Hogbom's nepheline syenites of Alno, by Andrews' New England 

 bathyliths, and many other occurrences to verify that alkaline 

 rocks can be produced by assimilation. The work of Jaquet, 

 Card, Harper, Mingaye, and White on the Kiama-Jamberoo 

 rocks is also much to the point. 



A^ain, the association of alkaline rocks with extremely calcic 

 rocks so often observed as in the Nandewar Mountains, and especi- 

 ally the sudden break from extremely basic gabbroic rocks and 

 peridotites which sometimes commence the cycle to extremely acid 

 alkaline rocks can hardly be explained by natural differentiation 

 processes. The later gradual passage from alkaline acid to calcic 

 basic rocks can well he explained on the differentiation-hypothesis. 



The existence of fragments of peridotite in alkaline rocks, as 

 shown by Siissmilch for the monchiquite of Bumbo Quarry, 

 Kiama, by myself for the lamprophyric monchiquite of the 

 Nandewars, by Derby in the Brazilian nepheline syenites, and by 

 Kraatzlan and Hackmann in those of Serra de Monchique is best 

 explained as I have done in dealing with the Warrumbungles. 



The general occurrence of the porphyritic habit and the uni- 

 versal occurrence of great resorption and corrosion of phenocrysts 

 in alkaline rocks show that crystallisation commenced in a deep- 

 seated reservoir, and on relief of pressure in rising to higher zones 

 the crystals were attacked by the ground-mass. 



The occurrence of graphic structure and sometimes micro- 

 graphic phenocrysts shows that eutectic conditions were first 

 reached in a deep-seated reservoir, then disturbed on the ascension 

 of the magmas, and finally reached again on cooling at the higher 



level. 



The evidence which all our alkaline trachytes so strongly afford 

 of pneumatolytic action displayed in the cryptovesicular structure 



