804 GEOGRAPHY OF BLUE MTS. AND SYDNEY DISTRICT, 



a maximum of sonic 400* feet only in the central portions. The 

 movement probably did not influence the streams materially, and 

 they immediately commenced to cut narrow canons near to base- 

 level in their old wide plains. Fig. d of PI. xxxix. illustrates the 

 appearance of the tilted Blue Mountain and Jenolan levels. The 

 rocks acted upon during this period were hard, consisting of 

 slates, quartzites and sandstones similar to those around Sydney. 

 Thus river-action was necessarily slow, especially in the final 

 stages. 



Stream-action continued for .such a period that the eastern 

 plateau as far inland as Wentworth Falls was cut down almost 

 in its entirety to sea-level, mere hillocks being left thence to the 

 coast, as may be seen to-day from the general level surrounding 

 Hornsb}'^ and Berowra. In the central plateau, as also the western 

 slopes, the hills had been attacked, and the plains on which 

 Orange, Blayney, Oberon, Wattle Flat, Hill End, Rydal and 

 Lithc^ow are situated, cut down almost to sea-level (PI. xxxix., fig. 

 e). Before the period closed the rivers wound and curved endlessly 

 through wide plains of their own making. Every time they 

 marched in serpentine course across the valle3\s the}^ attacked the 

 bordering hills, and widened their tracks. The channels in the 

 upper portions were filled with excessively rounded pebbles, 

 .capped by sand and mud layers. These pebbles consisted of the 

 hardest material only, such as quartz. These old streams, now 

 buried beneath lava flows, evidence oscillatory movements of the 

 plains, a fuller description of which is given in the author's 

 description of New England.! 



A period of volcanism is shown to be one of the closing events 

 in this cycle.; Explosion craters were formed, and long streams 



* This broad- bottomed valley near Lithgow, 400 to 500 feet below the 

 Blue Mountain heights, has been assigned by some to benching. 



t E. C. Andrews, " An Outline of the Tertiary History of New England," 

 Rec. Geol. Surv. N.S. Wales, vii., Pt. 3, 1903. 



X It is possible, however, that this will be proved to be referable to the 

 later carion cycle, as in the case of New England. Probably, also, many of 

 the old lava sheets round Bathurst, etc., originated in dykes. 



