236 O. A. hUSSMlLCH. 



undulating surface, but is bounded on both its eastern and 

 western margins by precipitous, rugged ridges ranging up 

 to 2,000 feet in altitude, and striking almost due north and 

 south. These ridges consist of Carboniferous lava flows, 

 whereas the low-lying region in between consists of Permo- 

 Carboniferous Coal Measures. Similar features continue 

 southward from Craven for at least another ten miles. 

 North of Craven this region is drained by the Avon and 

 Gloucester Rivers, as shown on the map in Plate XVIII. 



At Gloucester, which lies at the northern end of this 

 region, the lava flows of the eastern range, here known as 

 the Mograni Mountain, swing round to an east and west 

 direction, almost joining on to the western range— the 

 Gloucester Buckets — and almost cutting off the valley of 

 the Avon River at this point. 



At first sight, this long, narrow, relatively depressed 

 region might be taken for a rift valley, but a study of the 

 geological structure dispels this view. The Carboniferous 

 and Permo-Carboniferous strata have been folded into a 

 huge synclinal fold, striking north and south. The weak 

 coal-measures which lie in the trough of the fold have been 

 deeply denuded, whereas the Carboniferous lava-flows 

 which flank them on either hand have resisted denudation, 

 and have survived as steep ridges. 



In Tertiary times, a peneplain had been developed in this 

 district, and at the end of the Tertiary Period (the Kos- 

 ciusko Epoch) an elevation of about 2,000 feet took place, 

 converting the peneplain into a tableland. Denudation 

 since then has maturely dissected the tableland; mature 

 valleys have been cut into the weaker geological structures, 

 while the harder, resistant structures still survive as high 

 ridges. The way in which the larger streams cut across 

 the hard and weak structures alike, and the entrenched 

 meanders, notably those of the Barrington River, as well 



