PHYSIOGRAPHY OF THE SOUTHERN TABLELAND OF N.S.W. 353 



area lagged behind and now appear as relatively depressed 

 segments or "Senkungsf elder." The development of these 

 Senkungsfelder has brought about a considerable modifica- 

 tion of the pre-existing drainage systems, resulting in 

 extensive river-capture in the case of the Murrumbidgee 

 and Snowy Rivers and the formation of an inland drainage 

 area in the case of the Lake George Senkungsfeld. Above 

 the surface of the youngest peneplain (the Monaro pene- 

 plain) rise numerous residuals of two older peneplains. The 

 river valleys cut out during the existing cycle of erosion, 

 have not yet passed the early mature stage of development 

 and in most cases are still in the youthful stage of develop- 

 ment. The succession of events which has produced the 

 topography of this region may be briefly summarised (in 

 chronological order) as follows : — 



1. A cycle of erosion resulting in the formation of a 

 peneplain approximately at sea level — The Barren Jack 

 Peneplain. 



2. An uplift of about 500—600 feet converting the plain 

 into a plateau and initiating a new cycle of erosion. 



3. The second cycle of erosion with the production of a 

 second peneplain — The Mount Ainslie Peneplain. 



4. An uplift of 700 — 800 feet initiating a third cycle of 

 erosion, residuals of the older peneplain still surviving. 



5. The third cycle of erosion with the production of a 

 third peneplain — The Monaro Peneplain. This cycle of 

 erosion was less complete than either of its predecessors, 

 many residuals of the older peneplains surviving. 



6. A small uplift of about 200 feet followed by the form- 

 ation of broad mature valleys. 



7. Renewed uplift, ranging in amount from 1,800-6,000 

 feet accompanied by extensive faulting, and resulting in 

 the development of a number of fault blocks and Senkungs- 



