Art. XIII. — Supplementary Notes on the Diabase Rocks 

 of the Buckan District. 



By A. W. Kowitt, F.G.S. 



[Read 16th October, 1884.] 



On a former occasion I laid before the members of this 

 Society a paper on the Diabase rocks of the Buchan district.* 

 I was unable to speak at that time with desirable confidence 

 as to the exact position and character of some of the forma- 

 tions which I found at Murendel South. Since then, how- 

 ever, I have taken occasion to carry out further examinations, 

 and to collect materials for microscopic analysis of the 

 rocks. The results are embodied in these notes and in the 

 accompanying diagram section. I hope thereby to make 

 my former account of the Upper Buchan beds somewhat 

 more complete. 



For convenience of treatment I have arranged my subject 

 under the following sections : — 



The Quartz Porphyrites. — The lowest rocks which I 

 found at Murendel South are rough-textured, often massive, 

 and always dark-coloured (red or purple) igneous rocks. In 

 some places I have also observed just such rocks forming 

 the higher ridges, and in such cases their position is probably 

 due to the extensive faulting which has effected the district. 

 In the diagram section I show rocks of this kind at the 

 level of the Murendel River, and also at the summit of the 

 ridge marked (h). 



The rocks at the place marked (a) and (e) are rudely 

 bedded, and dip S. 30° — 40° W. at about 15°. I prepared 

 several thin slices of the samples I collected at (a) and (e). 



The ground-mass in these slices is crypto-crystalline, and 

 is apparently composed altogether of minute granules of 

 felspar and quartz, with some intermixed f elsitic basis, which 

 also fills in certain spots almost exclusively. In other places 



* Royal Society of Victoria, read 19th May, 1881. 



