Notes on the Geology of the Country around Goulburn. 65 



has already stated this fact. The colouring in the map shsws 

 the spots where this transition has been observed to occur. 



The granite and syenite require no comment as far as regards 

 their composition, but in addition to their association with the 

 quartz porphyry of Marulan, their intimate connection with the 

 stratified deposits deserves notice. 



At a spot on the Shoalhaven, a few miles below Nerrimunga 

 Creek, a bed of red granite, ten yards thick, known as the ' Red 

 Bar,' is interstratified with slates ; and higher up the river the 

 slates pass into red and white granite by such imperceptible 

 gradations, that it is impossible to determine where the stratifica- 

 tion planes of the slates end, and the joint planes of the granite 

 begin. The granite seems to partake of the strata's dip ; and 

 the same appearance of dip is presented by the granite in the 

 ravines of the dividing range west of Collector. In the granite 

 along the upper course of the Wollondilly, a well defined section 

 of its junction with stratified rocks is exposed, where the road 

 crosses the river near the Black Springs. The upper part of 

 this cliff section consists of chlorite schist dipping 35° W by S ; 

 and this is underlaid by thin bedded granite or gneiss with a 

 flaggy structure, and having the same dip. The bed of the river 

 above Pomeroy to its source, consists of a similar granite often 

 overlaid in the same way by schist and slate. 



The nest rock to allude to is the basalt. This rock, which 

 owes its origin to some ancient and long since obliterated volcano, 

 is un distinguishable in appearance from that of Pennant Hills, 

 which has been erupted through some of the youngest geological 

 strata on this side of the colony. It is generally massive, but 

 vesicular and amygdaloidal portions are often found. Its disin- 

 tegration affords a fertile soil, and the iron which it contains 

 imparts a chocolate or black colour to the ground. The waters 

 flowing off these areas are invariably hard, owing to the lime and 

 magnesia dissolved from the rock. The relation of the basalt to 

 the rocks surrounding it has not been traced in all classes. In 

 the gorge of the Shoalhaven, where the torrent has laid bare the 

 rocks, a small basalt patch, six miles south of Bungonia Creek, 

 was seen to be eruptive. Prom the fact of the basaltic areas 

 N.E. of Lake Bathurst occupying levels below that of many 

 surrounding parts, I am inclined to consider them eruptive too. 

 On the dividing range in the N.W. of the county the basalt 

 forms an overspreading mass ; it is found on the hill-tops only, 

 and not in the valleys. 



The Wollondilly has cut its channel through this overspreading 

 sheet of basalt, and has also excavated the schists and granite 

 below to a considerable depth. At Pomeroy the basalt lies 225 

 feet above the river, and at Pejar 300 feet. This basaltic area 

 in the N.W. possesses contour boundaries. Springs often issue 

 j 



