66 Notes on tlie Geology of the Country arowhd Goulbum. 



at the junction of the basalt with the underlying rocks, such for 

 instance as the Black Springs near Pomeroy. 



The greenstone areas, coloured brick-red on the map, are pur- 

 posely distinguished from the basalt, because the difference in 

 their characters, and the mode in which the greenstone is 

 associated with the stratified rocks, being either eruptive or 

 interbedded, make it doubtful whether it can be grouped with the 

 basalt as a product of the same series of igneous events. 



The conglomerate of the coal formation, indicated black on the 

 map, can be observed on the right bank of the Shoalhaven, east 

 of Bungonia, capping the loftiest summits of the ravine, exceed- 

 ing 1500 feet above the river. It here rests unconformably upon 

 the older strata indicated by the yellow colour. The same con- 

 glomerate stretches horizontally over much of the districts of 

 TJringalla and Eden Forest, but it here reposes upon unstratified 

 masses of syenite and quartz porphyry. On the railroad a few 

 miles east of Marulan, this conglomerate can be seen forming 

 bluffs along Barber's Creek, and it is also conspicuous on the 

 road side at Wingello. A range of hills formed of this con- 

 glomerate associated with sandstone, runs from near Marulan 

 Railway Station northwards to the Wollondilly Valley. The 

 river has cut its way through both it and a considerable thick- 

 ness of the underlying quartz porphyry ; and as the hard con- 

 glomerate occupies the upper portions of the hills and weathers 

 on all sides with steep or precipitous faces, it forms a bold 

 feature in the scenery of this part. One of these conspicuous 

 eminences overlooking the Wollondilly has received the name of 

 Gibraltar Rock. Here the conglomerate exhibits a thickness of 

 200 feet, reposing upon quartz porphyry, and setting in 200 feet 

 above the river's bed. It is composed of sand, pebbles, and 

 boulders ranging up to a foot in diameter, all firmly cemented 

 together. Its colour is white. The pebbles in it are chiefly 

 quartz and quartzite, and occasional rolled fragments of the 

 underlying quartz porphyry, which tend to show that the meta- 

 morphism of the older strata had occurred long before the 

 materials of the conglomerate were thrown together. The con- 

 glomerate represents an ancient sea-shore belonging to the epoch 

 when the glossopteris and other New South Wales coal plants 

 were flourishing. 



SECTIONS. 



Combined with the preceding remarks, the sections exhibited 

 will explain the geological character of the country. 



The first section starts from the eastern boundary of the 

 county at the junction of Nerrimunga Creek with the Shoalhaven 

 River, and crossing to the westward, making a little north, it 

 cuts first through the broken di strict of Inverary, passes a mile 

 to the south of Bungonia, then over the range forming the 



