Notes on the Geology of the Country around Goulbum. 59 



Immediately west of Lake Bat hurst, the Mulwarree commences 

 and forms a chain of ponds extending northwards to Goul- 

 bum, where it joins the Wollondilly. Its course lies through a 

 wide alluvial plain, which in most parts is naturally clear of trees ; 

 it is shut in by two parrallel ranges of hills already indicated. 



The Shoalhaven is the largest river in the county ; it flows 

 from south to north along the boundary, and finally turns off to 

 the eastward. This river and its tributaries flow through deep 

 gorges, and the whole bordering country has been carved by 

 torrents into a perfect network of deep and intricate ravines. 

 The Boro Creek, a tributary forming the southern boundary of 

 the county, passes through an alluvial plain for the last few miles 

 of its course, and presents at its junction a remarkable contrast 

 to the grand defiles by which the tribuiaries lower down, such as 

 the Nerrimunga and Bungonia Creeks, join on to the main 

 stream. 



The elevation above sea level of the junction of the Boro Creek 

 and Shoalhaven appear from aneroid observation to be 1900 feet, 

 the junction of Nerrimunga Creek 700 feet, and the river five 

 miles above Bungonia Creek 450 feet. All other river courses in 

 the county have a much greater elevation. 



The Wollondilly, near its source, was found to be 3000 feet ; 

 at Pejar, 2500 feet, at Pomeroy, 2230 feet ; at Q-oulburn, 

 2000 feet. 



The Mulwarree Ponds, at their commencement near . Lake 

 Bathurst, 2250 feet. 



These heights are only rough approximations. The drainage 

 of a small shallow saucer like depression, shut in by low hills 

 between the heads of the Mulwarree and the Boro Creek, but 

 not having an outlet into either, forms Lake Bathurst, which is 

 about 2,200 feet above the sea. I believe Lake George is about 

 2100 feet above sea level ; the lakes Tarago and Wologorong are 

 about 200 feet higher. 



DISTRIBUTION OP ROCKS. 



Turning now to the geology, the yellow colour of the map is 

 meant to indicate the areas where the rocks at or near the sur- 

 face consist of metamorphosed arenaceous and argillaceous strata ; 

 on the ridges these rocks often crop boldly out at the surface, 

 but in many other parts they are buried under deep alluvial soil, 

 or else capped with iron ore, or some comparatively recent deposit. 

 These rocks exclusively occupy the south-east corner of the 

 county, and in fact nearly its entire southern boundary ; they 

 stretch as a broad central belt right through the county from 

 south to north, exhibiting, however, some important interruptions 

 along the borders. On the west border granite and basalt occur 

 — coloured carmine and green respectively. These rocks occupy 

 the west of the county, and form the dividing range separating 



