Aet. XII. — Notes on the Area of Intrusive Rocks at 



Dargo. 



By a. W. Howitt, F.G.S. 



(Read 14th October, 1886.) 



Introduction. 



In a former paper on the geology of the Ensay district* 

 I gave a short section extending westwards from the range 

 on the eastern side of the Tambarra River to Mount Bald- 

 head. If that section had been extended still further to the 

 west it would have shown a tract of lower paleozoic rocks 

 between Mount Baldhead and the range separatmg the 

 waters of the Wentworth and Dargo rivers ; thence an 

 extended tract of intrusive quartz- diorites to a little west of 

 the Mitchell River, and finalJy Silurian rocks to where, at 

 Castle Hill, they are overlaid at a low angle by Upper 

 Devonian formations. The sketch-section, Plate III., ap- 

 pended to these notes, gives the part between the eastern 

 watershed of the Dargo River and Castle Hill. 



A little to the south of the above-mentioned line of section, 

 but parallel with its general course, there is a second out- 

 crop of intrusive granitic rocks, which extend westwards to 

 a point about south of Castle Hill. To the northward of 

 these intrusive areas, which form an almost continuous 

 series from the valley of the Tambo Kiver, there is an 

 unbroken stretch to beyond the Great Dividing Range of the 

 Silurian formations, where the intrusive rock masses again 

 are met with, rising in Mount Buffalo to the height of over 

 5600 feet above sea-level. To the southward of the line of 

 section referred to the lower paleozoic sediments extend 

 beyond Tabberabera, where they are overlaid by the Upper 

 Devonian rocks, and again reappearing at Boggy Creek, are 

 there seen to have been broken through by enormous masses 

 of porphyritic granitic rocks, the denuded summits of which 



* " The Sedimentary, Metamorphic, and Igneous Rocks of Ensay." Royal 

 Society of Victoria. Read November 12th, 1885. 



