BY W. N. BENSON. 157 



Abj.gArij. Titanomorphite is very abundant, occurring in 

 irregular grains or in long saw-like rows, as if developed from an 

 ilmenite-plate. No undecomposed ilmenite remains. 



More common than this are rocks which might be termed pro- 

 terobases. They are more or less crushed and altered, and con- 

 tain a reddish-brown hornblende, which forms isolated grains or 

 peripheral intergrowths with the augite. The latter is generally 

 fresh and similar to that in the rock last-described, though its 

 optic axial angle may reach as low as 2V = 42°. The felspar, on 

 the whole, may be a little more acid. An outer zone of albite 

 sometimes appears around the andesine-kernel, but an exact 

 determination is rarely possible. Ilmenite is generally replaced 

 by titanomorphite, and a very little apatite may sometimes be 

 seen. The structure varies from granular to ophitic. 



These rocks differ from the post-peridotitic dolerites of the 

 Barraba district, and also from the spilitic group of rocks, though 

 their chemical analysis repeats most of the features seen in the 

 analyses of the spilitic rocks. 



General Discussion. 



The observations, of which an account has been given, raise a 

 number of interesting and difficult problems. The most striking- 

 feature of the whole series of the Devonian igneous rocks is their 

 richness in soda. This character they share with the spilitic 

 rocks of England, and it will be of interest to see how far the 

 explanations offered for the nature of these rocks are applicable 

 to ours, and what alternative views may be considered. 



Messrs. Flett and Dewey consider that the albite in the 

 British spilite-lavas is secondary(2). They believe it to have 

 been produced by a pneumatolytic change affecting the rocks 

 shortly after their solidification. Solutions, rich in soda, traversed 

 the rock, attacking, and replacing by albite, the originally basic 

 felspar, and, at the same time, changing the pyroxene to chlorite, 

 epidote, and calcite. The intrusive albite-dolerites are equally 

 albitised, but, in them, the pyroxenes are rather better preserved. 

 The secondary nature of the albite is seen by its spongy character. 

 Associated with the English albite-dolerites is a hornblende-pro- 



