218 ON THE GEOLOGY AND PETROGRAPHY OF BATHURST, N.S.W., 



overlooked when dealing with our geology. We are, for the most 

 part, accustomed to consider the material removed by denudation 

 as eventually carried to the sea. None of the material removed 

 by denudation from around Bathurst in Tertiary times ever reached 

 any sea. It was disposed of in the same way as is the vast amount 

 of material brought down each year by the Macquarie. None of 

 this material ever gets to the sea, but is deposited over the plains 

 between Dubbo and the Darling. " The precipitous and rugged 

 country about the Upper Macquarie, the chains of basalt capped 

 hills in the Bathurst district, and all the surfaces which form the 

 valley of the river down to Wellington, have been carved into 

 their present shapes by the subaerial influences of air, frost, rain, 

 and rivers. Near Dubbo we might draw the line which would 

 show the limit of deposition, denudation and deposition being 

 synchronous and co-equal. The basaltic hills referred to have 

 their representatives at Dubbo, but with their summits barely on 

 a level with the surrounding country."* Professor A. Geikie 

 describes geological features very similar to our own in a paper on 

 the "Tertiary Volcanic Rocks of the British Islands." Referring 

 to the ridge of Eigg, he says : — " In Eigg a fragment of the river 

 valley has been preserved solely because it has been sealed up 

 under streams of vitreous lava which could better withstand the 

 progress of waste. Thus the Scur of Eigg, like the fragments of 

 the older basalt-plateaux of Auvergne, remains as a monument 

 not only of volcanic eruptions, but of a former land surface, now 

 effaced, and of the irresistible march of those slow and seemingly 

 feeble agencies by which the denudation of a country is effected." 

 It is very probable that a columnar structure is developed along 

 the line of hills, but unfortunately there are no natural exposures 

 of this interesting phenomenon. A large opening has been made 

 nearly on the line of section A B, PI. xvi. Here the columns of 

 basalt show well. Many are curved in a peculiar manner, but for 

 the most part the columns are straight. Between the joints they 

 vary in length from two to seven feet. The cup and socket 



* J. Milne Curran, " Notes on Geology of Dubbo." P. L. Soc. N.S.W. 

 Vol. X. p. 170. 



