RELATION OF STREAMS TO GEOLOGICAL STRUCTURE. 61 



Now not merely the soft Permo-Carboniferous, but the 

 Carboniferous strata, of very varying degrees of hardness, 

 play important parts in the structural geology, especially 

 of the more easterly part of the Hunter Basin. In one 

 part of the area the dominating geological structure is the 

 great Lochinvar anticline, with a general south-south-west 

 pitch. This structure is composed of hard Carboniferous 

 rocks overlain by the generally softer strata of the Permo- 

 Carboniferous. The Carboniferous contains such weak 

 strata as the varve rocks on a number of different horizons* 

 and the generally hard lava flows, tuffs and fluvio-glaciai 

 conglomerates. The Permo-Carboniferous strata are 

 dominantly softer rocks, with occasional harder horizons 

 such as the Ravensfteld Sandstone. 



Again, elsewhere, especially on the northern bank of the 

 Lower Hunter, the strata are mainly Carboniferous, con- 

 taining both hard and soft members, the strike showing in 

 some cases a suggestive correspondence with the courses 

 of tributaries. 



It must be borne in mind, further, that both Carboniferous 

 and Permo-Carboniferous strata have suffered considerable 

 faulting, which has in all cases produced lines of weakness, 

 and has sometimes brought soft Permo-Carboniferous strata 

 into contact with hard Carboniferous rocks. 



It is hardly to be expected that all these factors have 

 been without considerable influence on the development of 

 the river and its tributaries, especially as the whole basin 

 is in a state of mature erosion. Indeed Andrews seems to 

 believe that the straight course of the Goulburn-Lower 

 Hunter river, as well as the low altitude of the divide at 

 Cassilis are both due to a fault which lowered the height 

 of the divide as compared with the New England and 

 Central Tablelands, and formed a line of easy erosion for 



