FLOOD SILT OF THE HUNTER AND HAWKESBURY RIVERS. 



199 



Per cpnt. 



Volatile matter = 9*61 



Nitrogen = '084 



Weight per acre, one foot in depth = 3,403,125 lbs. 



Analysis of Silt from Haiukesbury River Water. 



Per cent. 



Insoluble in hydrochloric acid =89*96 



Soluble in hydrochloric acid — 



Oxide of iron and alumina (Fe 2 3 and A1 2 3 ) = 4*77 



Lime (OaO) = 0*49 



Potash (K 2 0) = 0*12 



Phosphoric acid (P 2 5 ) = 0*08 



Volatile matter = 4*68 



Nitrogen = 0'105 



Weight per acre, one foot in depth = 3,307,332 lbs. 



Assuming an average based on Mr. Prentice's observa- 

 tions of 2 inches of deposit after the subsidence of a flood, 

 the silt left by the Hunter River in flood would amount to 

 567,186 fbs. in weight per acre, and would supply the land 

 with a top dressing of fertilising constituents to the follow- 

 ing amount per acre : — 



Lime 8,791 lbs. 



Potash 510 „ 



Phosphoric acid ... ... 1,020 ,, 



Nitrogen 476 ,, 



A manuring which contains sufficient of the necessary 

 plant food to supply the requirements of most crops for 

 nearly 10 years. 



On the assumption that the same volume of water was 

 flowing for the same length of time at the same rate in both 

 cases, the amount of deposit left by the flood will be pro- 

 portional to the amount of suspended matter. Taking 2 

 inches to be the depth of deposit left by the Hunter River, 

 then the Hawkesbury River would deposit under the similar 

 conditions as to time, volume and rate of flow to- inch silt. 



