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to cross the Main Divide by following the thalwegs of the 

 Australian streams. Only when they turned their atten- 

 tion to the leading spurs, however, were the Blue Moun- 

 tains scaled. Some years later both New England and the 

 Darling Downs were discovered by adopting the same plan. 

 IV. Valley and "Lead" Topography. 

 (A) The evidence of the Valley Systems. -Coming from 

 the east, one notices that the intensely blue water of the 

 deep sea rapidly changes to duller hues when within a few 

 miles of land. The continental shelf thus entered upon is 

 narrow, the shore portion being roughened by islands.' The 

 shoreline topography shows harbours, lagoons, coastal plains, 

 raised beaches and lines of marine erosion. The rivers 

 have silted up their lower channels in great measure, but 

 harbours receiving inconsiderable drainage still possess 

 great depths of water. Bridge building operations along the 

 lower Hawkesbury River show a depth of 250 feet at least 

 of shore line submergence. Following one of the typical 

 main water courses inland, the drowned portion is found 

 to end at distances of from 60 to 80 miles from the shore 

 line." Hence the stream rises by slight rapids on to an 

 older valley floor. 



At varying distances from the sea a torrent track is 

 entered upon and the valley becomes a profound canon 

 varying in depth from 1,000 to 4,000 feet according to the 

 plateau traversed. These gorges are generally of "valley 

 in valley" type, and their sides are clothed with dense 

 growths of magnificent vegetation. With progress upstream 



