562 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS, 



may be as late as Cretaceo-Tertiary. No dykes of them have 

 been noticed in the Triassic strata of the district. However, 

 Triassic rocks do not occur in the immediate vicinity, so that 

 this fact is of doubtful value. The intrusive rock is remarkably 

 uniform in character, and Mr. Card has informed me that it is 

 extremely like the tinguaite from Abyssinia described by Prior. 



Leucite basalts have been described from Byerock and El 

 Capitan near Cobar, N.S.W., by Messrs. David and Anderson.* 

 The Rev J. M. Curran had previously written a note on leucite 

 basalts from these localities. t In 1891, J. M. Curran described 

 another leucite basalt from Harden, N.S. W.J 



The Byerock and El Capitan leucite basalts are considered to 

 be of Tertiary age, and they burst through Silurian slates and 

 the granites intruding the Silurian. 



Stonier§ has described a leucite basalt occurring in similar 

 country at Lake Cudgellico. 



The chemical composition of some of these rocks is given in the 

 Records of the Geological Survey of N. S. Wales 1904, Vol.viii. 

 They are so constituted that they might well have been derived 

 by an ultrabasic magma having assimilated a stratum extremely 

 rich in potash. 



Nepheline Basalts. — Mr. G. W. Card has described a 

 nepheline basalt from the Capertee Valley. || This rock intrudes 

 the Permo-Carboniferous, but has not been noticed to pass into 

 the overlying Hawkesbury — hence its age may or may not be 

 greater than the Hawkesbury. Like the Cambewarra volcanic 

 rocks, it lies on the rim of the Sydney coal-basin. Mr. Card has 

 also identified nepheline in Post-Triassic basalts of the. Hawkes- 

 bury area.U 



In a south-west direction from Sydney around Mittagong and 

 Bowral we have a group of trachytic intrusions and necks which 



* Records Geol. Survey of N.S. Wales, 1889, Vol. i. Part 3. 



t Proc. Linn. Soc. N.S. Wales, 1887, p.974. 



X Journ. Proc. Roy. Soc. N.S. Wales, xxv. p. 2 10. 



§ Records Geol. Surv. N.S. Wales, Vol. iii. Pt.3. 



|| Loc. cit. Vol. vii. Pt.2. 



11 Lot. cit. Vol. vii. Pt.3. 



