BY W. N. BENSON. 



139 



117.Spilite, Frenchman's Spur, Nundle. (See Partiii., p.704, N.T.415). 

 1002.Dolerite, Munro's Creek, Bowling Alley Point. 

 1021.Quartz-dolerite, Munro's Creek. 

 145.Quartz-dolerite, Hanging Rock. (Part iii., p. 704, N.T.237). 

 1109.Variolite, Munro's Creek. 

 1013.Keratophyre, Hanging Rock, Nundle. 

 1086.Magnetite-keratophyre, Hyde's Creek. 

 1107.Dolerite in Serpentine, Chrome Hill, Bowling Alley Point. 



53. Average composition of all basalts. (Dal}', "Igneous Rocks and 

 their Origin," p. 27). 

 Miner alogical composition. — The high percentage of soda is 

 expressed in the very acid nature of the plagioclase developed. 

 If we calculate the composition of the felspar, assuming that all 

 the orthoclase plays the role of albite in the plagioclase, we have 

 the following table : — 



No. 117. Felspar Molecules. 



No. 1002. Felspar Molecules. 



No. 1021. Felspar Molecules. 



No. 145. Felspar Molecules. 



Or^AbgoAnso or Ab^^An^g 

 Or^Aby^Ango or Ah^^An^^ 

 Or9Ab68An32 or Ab73An2y 

 Or^oAbgyAnis or AbggAnjo 



Thus all the felspars, with the exception of the last, are oligo- 

 clase-andesine; the last is albite. Optical tests, however, show 



