CxVI. IRRIGATION GEOLOGICALLY CONSIDERED. 
rivers, and decomposed basalt probably enters largely into 
their composition. They are of a bluish-grey colour, and 
strongly plastic in character when wet, forming a serious 
impediment to travellers. When dry it becomes easily 
pulverised but forms a good road. 
Black Soils.—These are more tenaceous than the flood 
loams, and as described elsewhere by one of us,’ are typi- 
cally developed at Moree, *‘ where it is largely made up of 
decomposed basalt.’’ Lower down the Darling it is not so 
dark in colour and merges into the flood loam. ‘* With a 
fair amount of rain it is an extremely fertile soil—much 
more so than the red soil—but owing to its stiff clayey 
nature it is much more difficult to work.” After light 
rainfall this soil, on account of its extreme tenacity, is 
even more difficult to travel over than the flood loam 
country. 
The following is an analysis of typical flood loam by 
Mr. . 6B. Guthrie. F.C... i .C.S.5— 
Locality, Collarendabri. 
Nature of soil, heavy black loam. 
Reaction, alkaline. 
Capacity for Water, 53°6. 
Mechanical Analysis—Root fibres and stones, none; 
coarse gravel. 0°25; fine gravel, 0°83; sand, 35°60; 
clay, 0a°a2. 
Moisture, 5°69. 
Volatile Matter, 6°17. 
Nitrogen, °05. 
Soluble in Hydrochloric Acid—Lime, 1°00; potash, °55; 
phosphoric acid, °07. 
Red Soils.—These soils are in marked contrast to the 
black soil on account of their lighter and more porous 
= 
+ Mineral Resources of New Scuth Wales, p. 466. 
