385 



an original cross-hatch twinning, indicating that some of the original felspar 

 phenocrysts were microcline, though indeed such a feature may be developed in 

 orthoclase under stress. The base material is granulitic, and so fine grained as to 

 be difficult to resolve, though small scraps of biotite are easily discernible through- 

 out. The rock was originally a quartz-felspar porphyry with felsitic base. 



A second specimen from the vicinity of Willigan Hill is a more severely 

 altered form of the same rock. The eyes of blue quartz stand out clearly, but 

 the base and the felspars have been granulated to such a degree that the rock 

 is distinctly a schist, in which minute scales of dark mica figure prominently, 

 imparting a dark colour and micaceous appearance to the entire rock. 



Two erratics of an almost identical quarts-felspar-porphyry were found 

 during the same expedition in the tillite at Red Hill. 



In the hard specimen these are light-grey rocks of a microcrystalline char- 

 acter, with the exception of porphyritic quartzes and felspars. The quartz 

 phenocrysts are smaller than usual in the Mount Painter Belt porphyries, and in 

 one of the specimens are comparatively scarce. They exhibit merely a sug- 

 gestion of the blue optical effect which characterises the closely similar rocks of 

 the Willigan Hill neighbourhood. Relics of orthoclase and microcline pheno- 

 crysts are numerous in both specimens, all recrystallized as dusty aggregates. 

 The base is a very fine-grained granular mass composed of clear granules like 

 quartz with a sprinkling of biotite and a little muscovite. Strain features are 

 shown by the porphyritic quartzes. The close correspondence between the rock 

 of these erratics and that described above, collected in situ, makes it practically 

 certain that they originated from the neighbourhood of Freeling Heights. 



The Acidic Pneumatolitic and Hydatogenous Intrusion of the Giant's 

 Head and Tourmaline Hill near Umberatana. 

 Though removed some few miles from the Mount Painter Belt proper, there 

 is a very remarkable and abnormal intrusion extending at least for a very 

 considerable length at no great distance from the road leading from Umberatana 

 to Yudanamutana. It has a general west t6 east extension. The Giant's Head, 

 near to and approximately south-east of Umberatana Head Station,- is the 

 western extremity of the formation. According to Mr. W. B. Greenwood, to 

 whom reference has already been made, the intrusion continues to the eastward 

 practically without a break until it merges into the Mount Painter complex. 

 There was no opportunity of checking this statement. When examined at the 

 Giant's Head, the intruded rocks of the Adelaide Series, not far below the 

 tillite, are arched up and metamorphosed for a distance of a quarter of a mile 

 from the contact. The metamorphic rocks thus produced are chiastolite schist, 

 actinolite schist, tremolite schist, and silicated limestone. Also a little copper 

 pyrites associated with haematite was noted in dolomite in the vicinity. At this 

 point the dyke has a width varying from 25 to 80 yards. The rock has all the 

 characteristics of a low-temperature formation rich in gaseous and volatile 

 components. It was from a patch in this formation that a fetid felspar was 

 collected by Mr. Howchin and described by the present writer. ^^^> Striking 

 formations of graphic quartz and felspar and graphic tourmaline and quartz 

 are to be seen. In some areas where the rock is composed of granular quartz 

 and felspar it is of a quite porous nature, and it is in just such places the 

 quartzes and felspars are most notably charged with liquid inclusions, a con- 

 stituent of which included matter is hydrogen sulphide, which imparts the fetid 

 character to the rock. A coarse-textured pegmatitic formation cuts across the 

 formation in one place and carries crystals of sphene noted up to 6 inches in 

 length. 



(") Trans. Roy. Soc. S. Austr., xxx., 1906, p. 67. 



