and Igneous Rocks of Ensay. 109 



occurrence of a number of oval or irregularly-shaped serpen- 

 tine pseudomorphs, in which no trace of the original mineral 

 remains. Did they occur, for instance, in a basalt, I 

 should feel very little doubt as to their representing olivine. 

 This rock is probably a granitite. 



40. — I collected this sample on the summit of the 

 mountain, on the eastern side of the Tambarra River, where 

 it shows out in large masses. It has the following composi- 

 tion : — (a) Mica, which is reddish brown with ordinary 

 transmitted light in basal sections. In those parallel to the 

 "c." axis it is dichroic, when examined over the polariser, in 

 shades of brown and yellow. The only inclusions are 

 magnetite crystals. The alteration is to chlorite, (b) 

 Orthoclase. (c) Triclinic felspars, in crystals, which are 

 better formed than the orthoclase, and compounded accord- 

 ing to the Albite law. The few measurements of obscura- 

 tion angles which I could obtain were not satisfactory, being 



in the zone OP — oo P oo, between 2° 30' and 24°. 

 The alterations of all the felspars are micaceous, (d) 

 Residual quartz, of the usual kind in such rocks, (e) 

 A little apatite, and rarely titanite. This rock is also a 

 granitite. 



Principal Characteristics of the Rocks. 



I have now described at some length the mineral composi- 

 tion of the rocks which I have found along a line of section 

 crossing the Ensay district. These rocks fairly represent 

 the formation of the whole district, of which Ensay is the 

 central part. 



It will now be well, for the sake of clearness, to summarise 

 the principal and characteristic features of these groups of 

 rocks, before proceeding to consider how they are related to 

 each other. 



It is to be first noted that the sediments which I have 

 described have not the normal mineral character of the least 

 altered Silurian formations of North Gippsland. These latter- 

 are best seen in tracts where there are no signs of the nearness 

 of intrusive plutonic masses — as, for instance, in the valleys 

 of the Wongungarra, or the Thomson River below the 

 crossing of the Walhalla-road. 



The mineral condition of the argillaceous and arenaceous 

 beds in such localities is most certainly not such as one can 



