144 G. D. OSBORNE. 



be seen in the South Coast area. Certainly under the 

 microscope there is a big textural difference, but chemical 

 comparison is difficult owing to the decomposed state of 

 the rocks. 



The inclusions in dyke No. 1 have been interpreted on 

 precisely the same lines as those laid down by Dr. Benson 

 for Dundas. These rock types vary from norites right 

 through with decreasing acidity to dunites, including, the 

 rock troctolite, recorded in this State for the first time. 

 The rare association is found of pleonaste and augite in 

 olivine-bearing gabbroid rocks, and also a unique inter- 

 growth of augite and picotite in a harzburgite. The 

 differentiation which produced the phases, later torn up 

 into fragments and carried to higher levels, may have some 

 features directly explicable on Bowen's theory of differen- 

 tiation by sinking of crystals. The ultrabasic rock types 

 very probably represent a phase, derived by differentiation 

 in an intercrustal reservoir from a magma, which itself 

 was a differentiation product from an alkaline magma. 



Amongst the inclusions not cognate in nature, there are 

 examples of gneissic? granite derived from an ancient 

 terrane, and rhyolitic rocks possibly referable to the 

 Carboniferous Volcanics (Kuttung Series) which may prob- 

 ably extend underground as far south as the Basin. A 

 third type is of a certain fragmental calcareous rock which 

 may have been part of an upper Mesozoic unit. 



Veining the igneous rocks at the Basin there occur satin 

 spar, quartz, calcite and aragonite. 



Acknoivledgements. — In conclusion the writer wishes to 

 thank those who have helped in matters connected with 

 the preparation of this paper* To Professor David he is 

 indebted for advice on many points, and for constant 

 sympathetic interest. He has profited by discussions with 



