800 GEOGRAPHY OF BLUE MTS. AND SYDNEY DISTRICT, 



Jenolan residuals were always favourably situated as regards 

 their own preservation. During the formation of the Blue 

 Mountain peneplain, the process of " adjustment of streams to 

 structure" had to be started again, but during the Blue Mountain 

 cycle the repeated migrations of the streams had searched out all 

 but the strongest structures. Then in the successive Lithgow 

 Period the loss sustained by these Lambies* was trifling, such 

 wear as they show being expressed by the formation of moderately 

 sized valle}^s only, their position and hardness allowing of their 

 preservation amid the general destruction. During the canon 

 C3^cle a series of deep valleys was carved in the shallow basins of 

 the previous period, mainly as the result of pronounced elevation 

 in forcing underlying weak structures high above sea-level. 

 Examples of these cafioned mesas are the deep gorges at Jenolan 

 and Kowmung (Kanangra) and the Macquarie River Valle}^, 

 broad in the vicinity of Bathurst and contracted along its lower 

 northern course in a gorge. In the case of the Macquarie River, 

 a dome-shaped mass of granite (suggestively laccolitic in appear- 

 ance)! is responsible for the weakness, the granite itself being 

 resistant, but the weaker contorted Silurian slates overlying the 

 boss were "stripped off" during the early age of the canon cycle 

 by the river in its lateral migrations, and these wanderings by 

 discovering the continuation of the weaker rocks underlining the 

 Devonian quartzites of the survivals from the Jenolan denuda- 

 tion, set up sapping, which operated so as to cause the rapid 

 retreat of the precipitous escarpment of the Jenolan mesas at the 

 Stony Ridges and Clear Creek. 



The Plateaus. 

 1. The Jenolan Plain. —^\\\e Mountain studies reveal the fact 

 that at some stage in the earth's history — which we have named 



* The Americans employ the term " Catoctins " for the um-educed masses 

 in the present cycle, and " Monadnocks " for those of a cycle previous to the 

 present one. The writer proposes the name " Lambies " for the residuals of 

 the third cycle, and " Spiribies" for those of the fourth, from Mts. Lambie 

 and Spiriby, two conspicuous peaks of the Jenolan and Capoompeta levels 

 respectively. 



t J. C. Ross, Q.J.G.S., Vol. 50, 1893. pp. 105- 119. 



