The base of the Murray gorge a score of miles below 

 Kosciusko (7,300 ft.) is 6,000 feet below the same plateau 

 surface. 



The Hawkesbury is 330 miles in length. Near its source 

 the plateau has been faulted, the Jenolan horst to the 

 west is about 3,500 feet in height and the lower faulted 

 mass is about 2,600 feet in height. Along this lower level 

 the upper Hawkesbury or Wollondilly flowed until such 

 level was dissected by the headward recession of the stream. 

 The Wollondilly now occupies a V shaped gorge in the 

 porphyry plateau, the base of the gorge being only 600 feet 

 above sea level, even as much as 200 miles up stream. 



The canons of the Macleay headwaters are 2,000 feet 

 deep a few miles below the commencement of their torrent 

 and waterfall stages. 



The Bellinger western headwaters descend 1,000 feet 

 within a distance of 10 miles, and 5,000 feet within a dis- 

 tance of 30 miles. In the case of the Bellinger, however, 

 this wonderful dissection lias been aided by block faulting. 

 The view from the fault block is one of the most impressive 



The South Clarence is only 280 miles in length, but at a 

 distance of 150 miles from its mouth it is only 300 feet 

 above sea level, while the plateau surface to the immediate 

 west is about 4,000 feet in height. 



Equally striking facts of dissection may be cited for the 

 north coast of Queensland and Tasmania. 



(b) Stage of dissection.— Profound as are the canon 

 depths which score the plateau surfaces, nevertheless the 

 stage of such dissection is a very youthful one. Although 

 the coastal streams have such short courses yet their 

 canons have not retreated to the Main Divide, except in 

 one or two places, as at the Liverpool Range in New South 



