174 THE GKOLOGY OF DUBBO, 



and slaty and not unlike some uppei* Silurian and Devonian beds 

 in other parts of the Colony, are inclined at an angle varying 

 from 58*^ to 63° dipping to the north-west. This is the only 

 instance of the kind in the district. It is not impossible that they 

 might represent the older rocks appearing again at this the other 

 extremity of the basin. I could find no fossils. A more probable 

 opinion is that they are part of the Dubbo series, tilted to their 

 present position by an outliurst of basalt. The nearest visible 

 rock is granite, but for many reasons it is impossible to think the 

 granite of later origin than the sandstones. The inclined rocks 

 form an isolated hill, a fact which increases the difficulty of 

 determining either their relative age or the cause of the disturbance. 

 An additional interest is attached to these beds from the fact that 

 they dip under the great plains at this point. 



Basalt covers about one tenth of the area of the country imme- 

 diately around Dubbo. The isolated patches on the right bank of 

 the river are part of one great stream that flowed down the old 

 river valley. The basalt on the left bank of the Macquarie seems 

 to be an older flow. A wall of vesicular basalt 40 feet in height 

 may be seen on the Mogrigui Creek. 



On Gearie Station near Murrumbidgeree there is an isolated 

 conical hill, which is I have no doubt an old volcanic " neck," It 

 is very different from the usual table-topped basalt-crowned hills 

 that may be seen from its summit, and which are the remains of a 

 great basaltic plateau. 



A peculiar appearance is often presented when the surface of the 

 basalt is weathered into a gentle slope. The surface of the ground 

 resembles a ploughed field. The ridges are always parallel but often 

 curved at sharp angles, though still preserving their parallelism. The 

 average height of the ridges is about five inches or less from crest to 

 troiigh, and they vary in width from six to eighteen inches. No 

 satisfactory explanation as to the cause has yet been given. I 

 would suggest that the appearance is connected with the jointings 

 of the basalt below. The furrows do not always follow the incline 



