116 J. H. MAIDEN. 



seeds and plants to lower levels, e.g., Nut Grass (Cyperus 

 rotunclus), Yellow or Prickly Poppy (Argemone mexicana), 

 Yellow Indigo (Cassia spp.), Bathurst Burr (Xanthium 

 spinosum), Yellow Thistle ( Kentrophyllum lanatum), 

 Chinese Thistle (Centaur ea calcitrapa) and other thistles 

 and pests of various kinds. The undisturbed propagation 

 of weeds in the bed of an upper creek thus means loss to 

 any rich lands on a lower level. Therefore, although for 

 engineering purposes the consensus of opinion is to work 

 from Newcastle, my view as regards weeds prevention is to 

 begin as high up the Hunter and its tributaries as possible. 

 They not only float the seeds down, but nice rich silt to 

 give the weed-plants a fair start in life. 



VIII. Some Miscellaneous Factors in Erosion. 



a. Boulders. — The small stones and boulders in the bed 

 of a stream are set in motion by floods, and forming eddies 

 etc., grind down tlie banks. Good rich basaltic land is very 

 fine grained, and washes away readily. The stones which 

 are always found in it more or less help to break it away. 

 Sometimes they form masses of considerable weight. The 

 black soil everywhere rests on a bed of gravel. The water 

 gets underneath and through the black soil, these gravel- 

 stones facilitating the circulation of the water and the 

 disintegration of the superimposed soil. 



b. Dead trees. — The dead trees and branches felled for 

 stock, unless they are dry enough for burning before the 

 floods come, do much damage. So many River Oaks (and 

 other trees) have been cut down during the present drought, 

 that if a flood comes soon, enormous damage will be done 

 through these dead trees tearing down the creeks and 

 rivers. Dead timber of course threatens the bridges and 

 also churns up the banks and works destruction. The 

 courses of creeks are so irregular and the water comes 

 down so suddenly that a stream may become a succession 

 of grinding whirlpools. 



