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SOILS AND SUBSOILS OF SYDNEY AND SUBURBS. 

 By J. B. Henson, C.E. 



[Read before the Sanitary Section of the Royal Society, X.S. Jr., 13 Sept., 1887. .] 



The general health of a community is largely influenced by the 

 condition of the soil upon which the population is located and also 

 by the condition of the soil of the surrounding country. Soils by 

 their influence upon health are generally referred to as being 

 healthy or unhealthy. This classification is not based upon the 

 character of the mineral constituents of the soil, nor is the 

 percentage of organic matter or humus present a usual element 

 in its determination. But the condition of the organic matter, 

 mainly in respect to the extent to which oxidation has progressed, 

 is of vital importance and it is the condition of the organic matter 

 in the soil together with the amount of moisture present which 

 determine the unhealthiness. There are soils which are not 

 naturally very unhealthy, but which are of such a description as 

 to become readily contaminated by any organic refuse which may 

 be deposited on their surface. In the neighbourhood of dwellings 

 such contamination is likely to prove progressive and accumulative- 

 and serious results may ensue. 



Healthy soils are such as contain a minimum amount of organic 

 matters and are free, porous, and well drained. The ventilation 

 of the soil is essential to its preservation in a healthy condition. 

 This in porous soils takes place naturally at every change in the 

 atmospheric pressure, for concurrent with every change in the 

 density of the super-incumbent air a movement of the air in the 

 interstices and pores of the soil occurs. The entry of rain water 

 into such a soil displaces the air and as the water drains off air 

 re-enters. The aeration of the soil promotes the oxidation of 

 contained organic matter be it natural to the soil or derived 

 from outside sources. Soils containing an undue proportion of 

 decomposable organic matter, or which are dense, un ventilated 

 and wet, are unhealthy. Soils which exhibit a combination of 

 these two unfavourable conditions are very unhealthy. Excess, 

 of moisture in the soil is injurious to the majority of cultivated 

 plants and to the higher types of animal life particularly to- 

 man. Farmers know well that to raise good crops or to breed 

 healthy stock they must avoid wet soils and it is quite certain 

 that the land which an intelligent farmer would reject as too- 

 unhealthy for his purposes would be unfit for a dwelling site- 



