OCCURRENCE OF TINGUAITE AT KOSCIUSKO, N.S.W. 357 



nepheline as does the Kosciusko rock. The Barigan rock does 

 not exhibit flow structure among its felspar microlites, whereas 

 flow structure is well seen in the Kosciusko rock. The Barigan 

 rock moreover has numerous clear streaks, of the nature perhaps 

 of segregation lines, not seen in the Kosciusko rock. A subsequent 

 examination of the Barigan area by Mr. Oarne and Prof. David, 

 shows that these lines are related to directions of pressure in the 

 tinguaitic laccolites, the rock having a banded almost gneissic 

 appearance the bands being approximately concentric to the 

 general surface of the laccolites. 



The Barigan rock is essentially composed of nepheline and 

 segirine, with numerous, irregularly distributed microlites of felspar 

 and probably a little sodalite. Further information relating to 

 the petrological character and mode of occurrence of this highly 

 interesting rock from Barigan and the associated tinguaites will 

 be published shortly by the Geological Survey of New South Wales. 



II. Occurrence at Mount Kosciusko. — The tinguaite of Kos- 

 ciusko occurs in the form of a dyke traversing granite. The dyke 

 is about seven feet wide, is vertical or nearly so, as far as can 

 be seen in the small section in the bank of the creek, and 

 strikes in a direction E. 5° N. and W. 5° S. The height above 

 sea-level is about 5,600 feet. The spot where the dyke crosses 

 the creek [which flows from Lake Mere wether (Blue Lake), and 

 Hedley Tarn through Evidence Valley (Helms) to the Snowy 

 River] bears about E. 47° N. from the Kosciusko Observatory, 

 and is about four miles and thirty-nine chains distant. The spot 

 is about a quarter of a mile up Evidence Valley Creek from its 

 junction with the Snowy River. 1 



The rock on either side of the dyke is a slightly gneissic granite. 

 The granite extends in a westerly direction from Evidence Valley, 

 for about one mile, when it is replaced by a belt of phyllite and 

 fine quartzite. This belt is from about a quarter of a mile up to 



1 See Plate 2, for geological plan showing occurrence of dyke. See 

 also Proc. Linn. Soc, N. S. Wales, New Series, 1901, Pt. 1, PI. iii., and 

 pp. 30-31. 



