BY E. C. ANDREWS. 803 



tion. The very broad valleys of Lithgow and associated areas, 

 iind the 3000 feet level of the western areas appear to be against 

 this view. The writer also predicts differential erosion for the 

 coastal and more inland areas. 



The cycle of denudation which closed with the formation of the 

 Blue Mountain peneplain involved the operation of long-con- 

 tinued and slowl}'- acting forces. The streams wore the land 

 down approximately to the old age stage, and broad plains like 

 valleys were induced in all but the central areas of hard Palaeo- 

 zoic rocks (PI. xxxix., Hg. c). Compared with the Jenolan cycle, 

 however, during which the central portions had suffered wholesale 

 reduction, the Blue Mountain cycle was of short duration. 



The sequential stages in the coastal topographical development 

 after the uplift, resulted in a set of conditions very similar to 

 those obtaining at the completion of the Jenolan cycle. The sea 

 had, however, less time in which to accomplish its purpose. Thus 

 the encroachment on the land by the sea was less pronounced 

 than in the former gradation period, although the coastal and 

 shore-line features were very similar. 



Upper Cretaceous (?) History. 



The Lithgoiv Plain (The Plateau cycle). 



With the close of the Jenolan and Blue Mountain cycles, the 

 two longest chapters in the modern (geologically considered) 

 topographical development of the Blue Mountain area are ended. 

 The remaining chapters are, however, full of suggestion and 

 interest, inasmuch as minor movements can be read easily in the 

 recent cycles, while the main features alone are decipherable in 

 the Jenolan and Blue Mountain periods, facility of interpreta- 

 tion, as regards surface features, being inversely proportional to 

 the remoteness of time of any cycle of operations under consider- 

 ation. 



While yet the Sunny Corner and associated mountains 

 remained to evidence the former proportions of the Jenolan Plain, 

 another period of elevation occurred, this time, however, reaching 



