524 GEOLOGY OF THE CLARENCE RIVER BASIN, 



But to return to the conglomerate at the top of the Orara 

 range. It occupies an ancient river bed, now the summit of a 

 hill more than 900 feet above the sea. It is composed of pebbles 

 large and small, all well rounded, of ellipsoidal shape, and 

 composed of hard slates, &c, without quartz. It contains patches 

 of coarse sandstone, bedded at various angles, and composed of 

 river sand, with few, if any, separate grains of quartz. There can 

 be no doubt as to its fluviatile origin ; and it is probable that 

 it represents a somewhat deep portion of the bed, where the 

 shingle might have been consolidated by cement before the waters 

 had deserted that part of their course : for it seems clear that 

 this bed of concrete served to protect the portion of the range 

 immediately beneath it from the waste which the rest has suffered. 

 Again, down the eastern slope of the range we come upon other 

 shelves or patches of the same material, the pebbles diminishing 

 in average size, but otherwise the. same, until at last in the 

 bottom of the creek we see it emerging upon the right bank from 

 the loose shingle of the torrent bed, and forming, as has already 

 been said, the basis of the horizontal series. It is not to be 

 supposed that this conglomerate underlies that series throughout. 

 It is clearly, I think, a river shingle, and cannot be supposed to 

 extend very far to the eastward of OBX. Upon what then does 

 it rest, and what is the formation upon which the Clarence River 

 beds have been deposited ? The conglomerate showing first as a cap 

 to the range, secondly as a series of shelves upon the western or 

 left hand slope, and finally as the bottom rock of the escarpment 

 on the eastern or right bank, seems to give one half the answer ; 

 and the disappearance of the older rocks East of the range, to 

 complete it. I suppose the river which formed the upper con- 

 glomerate to have run northwards along a line of fault in the 

 Slates. This line is now marked on the map by the division 

 between the Silurian and Clarence River beds, and on the ground, 

 at least in part, by OBX Creek. I suppose further that the 

 lowering of the river was mainly due, not to erosion, which could 

 have had comparatively little effect upon a bottom so well protected 

 by deep shingle, but by the gradual descent of the whole country 



