Xotes on Obsidian (iiid Auslralites. 337 



alkalies, and also the " basalt " from the Coliljaii Kivtr, near 

 Kjneton, in which 61.96 % of silica, 10.43 % of iron, and only 

 2.10 % of alkalies are recordeil. Tliese are published in the essay 

 cited above, and ai-e quoted without coiuuient by Mr. Dunn. They 

 must be regarded as quite unreliable. 



The Taradale "obsidian." 



Associated with pebbles of black basalt along the course of the 

 Coliban River from the Upper Coliban Reservoir to Taradale, Mr. 

 Dunn found and has describedi well-rounded pebbles of what he calls 

 black obsidian. Mr. Dunn first found these pebbles at Taradale. 

 He quotes a first-class analysis made of this material by Mr. J. C. 

 Watson, of the Geological Survey Laboratory, and for comparison 

 the analysis by Mr. J. C. Mingaye, of N.S. Wales Geol. Labora- 

 tory, of a remarkable australite from Uralla, in N.S. Wales. 



The analyses are as follow, with another for comparison : — 



(1) Taradale (2) Uralla (8) Diorite 



Obsidian. Australite. Porphyry. 



SiO, 63.67 64.68 62 18 



AlA 15.83 16.80 15.77 



Fe,A 1-39 6.57 1.83 



FeO 4.06 1.01 2 44 



MgO 2.15 2.50 3.55 



CaO 3.88 3.88 4.13 



Na^O 3.57 tr. 3.92 



K2O 3.69 4.01 3.91 



H,0+ 0.02 — 0.70 



H^O- 0.15 — 0.30 



TiOa 1.27 — 0.55 



PA 0.02 — 0.32 



MnO 0.43 — BaO 0.43 



NiO and CoO 0.01 — — 



Total =100.14 99.45 100.23 



Sp. Gr. = 2.569 



3. Diorite Porphyry, Steam Boat, Little Belt Mt., Montana. Analyst, 

 W. F. Hillebrand. Desci-ibed by L. V. Pirrson. Recorded in Chemical 

 Analyses of Igneous Rocks by Washington, 1903, p. 222, United States 

 Geol. Survey. 



The Taradale rock is a remarkable one, and Mr. Dunn has done 

 a distinct service to Victorian petrology in drawing attention to it, 

 since it appears to be a type hitherto unrecognised among the recent 



1. Op. cit. 



