7 LVIII. CHEMICAL NATURE OF THE SOILS OF N.S.W. 
figures given by F. H. King, Professor of Agricultural 
Physics at the University of Wisconsin, in his book on ‘The 
Soil,’ contrasting the chemical nature of arid and humid 
soils. The figures are taken from analyses of Hilgard:— 
III.—Comparison of Soils from Humid and Arid Regions of the United 
States. (From F. H. King, ‘‘ The Soil.’’) 
Humus. | Nitrogen.| Lime. Potash. Dhaene 
Soils from humid regions...| 3°04 13 mt "22 ‘11 
Soils from arid regions 0°75 ‘10 1°36 ‘73 12 
In these figures it will be seen that the difference between 
the amounts of mineral plant-food are even more strongly 
marked than is the case with the figures dealing with our 
own soils. The explanation given by Professor King is the 
same as I have suggested, namely, “ that sufficient water 
falls for the decomposition of the rock, and the formation 
of alkalies and of zeolitic mineral ’’ (zeolites are soluble in 
hydrochloric acid), ‘‘but not enough to remove these when 
formed, as is the case in arid regions.’’ The fact that 
these soils are richer in mineral plant-food is one of con- 
siderable importance in relation to their fertility, though 
it must be remembered that richness in plant-food is only 
one of the elements of fertility, and that this property alone 
is not sufficient to render a soil fertile. 
Humus in American Soils.—A much more striking differ- 
ence in our soils and in those of similar soils in the States, 
as examined by Hilgard, is the relatively large amount of 
organic matter as compared with the “‘ humus” shown in 
Hilgard’s analyses. It must be explained that the organic 
or volatile matter in our analyses is not strictly humus only, 
but includes unchanged vegetable matter, small root-fibres, 
and so forth, which are sometimes present in these soils in 
considerable quantities. It also includes water of combin- 
ation and carbonic acid. The true humus—that is, the 
decayed vegetable matter—is certainly much smaller in 
