76 SECTIONAL ADDRESSES. 



Supply and Public Works, as indicated previously, but a few remarks 

 may be made to show how this is so. 



Agriculture and Forestry. — The growth of plants, whether grasses, 

 herbs or trees, is dependent on the chemical and physical properties of the 

 soil, on the configuration of the land, and on climatic and other conditions. 

 Since plant foods consist largely of certain rock-forming minerals in a 

 soluble condition it is necessary to know what is the chemical character of 

 the soil. This can be ascertained by analyses of samples collected by 

 geologists, for much of the value of the analyses depends upon a careful 

 determination of the types of rock forming the base of the subsoil. Where 

 such consists wholly of one kind, as granite or dolerite, and the soil is one 

 derived directly and wholly from it, a few analyses only are necessary to 

 give results which may be generally applicable to the whole area. But this 

 is not so with medium-bedded sedimentary rocks, comprising shales, 

 mudstones, sandstones, grits and conglomerates, and the chemically- 

 formed rocks, such as limestones, when these are of no great thickness. 

 The nature of the soil derived from them varies very much and depends 

 not only on the kinds of rocks — pervious or impervious — but also on their 

 disposition- — flat-bedded or inclined — and whether the ground is flat or 

 undulating. For the ascertainment of the character and disposition of all 

 these rocks the geologist is essential. 



There is, however, another aspect to be considered. Many soils are 

 not sedentary ones — derived directly from the underlying rocks — but 

 are soils of transport. The character of the soil, or even the subsoil, often 

 bears no genetic relation to the underlying rocks, and where such soil is 

 of no great thickness a geological knowledge of the rocks underlying is 

 necessary. In connection with irrigation the character of the soil of the 

 supply channels needs the attention of the geologist. He should note if 

 there is any crust of minerals on the soil, on the evaporation of water. If 

 so, these minerals should be analysed to see if they are those injurious to 

 plants, when in large proportion, such as certain sodium and magnesium 

 salts. This is important in areas with soil derived directly from rocks of 

 marine origin, particularly young clays, mudstones and sands deposited 

 in brackish lagoons and estuaries. If these minerals be present he may 

 be able to devise means by which the proportion of these harmful salts 

 when in solution can be steadily reduced by flowing away with the 

 water, and not being alternately and continuously precipitated and 

 dissolved. 



Water-Sufply. — This question of water supply is one that concerns 

 some colonies much more than others, but all are affected to some degree. 

 In cases involving the conservation of the water of annual streams, the 

 problem is dependent largely upon geological considerations. But where 

 underground water is sought, whether of the character of an artesian 

 supply, or due to seasonal rains, the problem is a much wider one, and may 

 be difficult to settle satisfactorily. For artesian water, not only the 

 configuration of the country, but also the disposition and nature of the rocks 

 must be known before any conclusion can be formed as to the chances of 

 success in obtaining such supplies. This is essentially a work for the 

 geologist, and even for him it is quite likely that the evidence available in 

 the district may be insufiicient — owing to the absence of natural sections 



