8 Notes on the Diabase Rocks 



Before entering upon details a few observations may be 

 admissible upon the physical features of the district wherein 

 the Diabase rocks occur. 



Physical Geography of the* District. 



That part of the district which is dealt with in this 

 paper lies between the Buchan and Snowy Rivers, and 

 immediately within the angle formed by their junction. 

 The area may indeed be imagined as a rudely equilateral 

 triangle, across the base of which extends the diagram section 

 accompanying these notes, while the apex is approximately 

 marked by the junction of the rivers. The country is 

 mountainous, but it is lower in elevation than the tracts 

 surrounding it. It is less rugged in outline, and it possesses 

 a better soil and is more richly grassed than the felsitic areas 

 amongst which it lies. This more favoured character is due 

 to the preponderance in it of the Buchan limestones, and of 

 the Diabase rocks which are the special subject of this paper. 



The characters of the two rivers, the Snowy and the 

 Buchan, which bound two sides of the area, differ consider- 

 ably. The former rises on the great table land of Maneroo, 

 and descends rapidly near the boundary line of the colony 

 through a deep rocky valley, excavated into indurated Lower 

 Silurian formations, and it thenceforward flows in a deep 

 and, generally speaking, a barren valley towards the sea. 

 The rocks in which this part of the valley has been exca- 

 vated are mainly varieties of intrusive granites, or of kindred 

 rocks of an acid character, such as felsites. More rarely 

 there occur tracts of Silurian sediments in a greatly inclined 

 and indurated condition. In that part of the valley which 

 lies to the east of Buchan there are small areas of limestone 

 which have been preserved by having been let down by 

 extensive and often well-marked faults. Near the junction 

 of the Buchan and Snowy Rivers there is a somewhat larger 

 outlier than usual of these Buchan limestones, and associated 

 with them is a still larger area of Diabase rocks. These 

 latter are dealt with in these notes. 



The settlement of Maneroo, the consolidation of the soil, 

 and the grazing down of the thick coat of natural grasses 

 by flocks and herds, the formation by stock of tracks and 

 by man of roads, has, for the last twenty or thirty years, 

 caused the rain falling on the great plateau to concentrate 

 more and more rapidly in the main drainage channel. So 



