MODEL OF NEW ENGLAND. 153 



that a study of the Hawkesbury, Shoalhaven and other 

 streams may reveal histories similar to those of the 

 Clarence, the Namoi, and the Peel. 



Another interesting feature may also be mentioned in 

 connection with these coastal streams. Whether mature 

 or youthful, they form "valley in valley" types. (The 

 western streams also exhibit the same feature). It is as if 

 the Stannifer (and Sandon) Peneplain surface had been 

 elastic, and, under periodic pressures, has swelled upwards 

 at several distinct periods, but so slowly as not to deflect 

 the streams from their main courses. This explains the 

 apparent anomaly of long north and south streams flowing 

 near the coast and turning suddenly to the east to enter 

 the sea. For the dense Palaeozoic structures had a general 

 north and south strike, to which, as mentioned already, 

 the acid granites formed no real exception. During the 

 peneplanation stages the weak structures were gradually 

 occupied by the streams, and the latter found it increasingly 

 difficult to cross the strike of the country. Upon the late 

 and great Tertiary Uplifts the streams found it easier to 

 follow the old channels than to carve new tracks across 

 the country grain. 



(c) The Inland Plains. — These have had a history very 

 similar to those of the coastal area. The western flanks 

 of New England are of Devonian and Carboniferous rocks 

 which proved to be relatively weak structures, and were 

 easily stripped from the more central granites. This is 

 well seen by a study of the model in the area drained by 

 the Gwydir, Namoi, Peel and Hunter Rivers. 



Biological Significance. 

 FjThe model tells its own tale to biologists. In late geo- 

 logical time the present plateau surface was several 

 thousands of feet lower. At that time there was no 

 plateau worthy of the name, a plain raised but little above 



