Agricultural Geology.

This subject is one on which the opinion of a botanist would carry more weight than that of a geologist, for the nature of the crops that can grow in a district depends more upon the climate than upon the mineralogical composition of the soil. It is also well known that owing to a variety of complicated causes, the soil of most countries varies considerably over very limited areas, and so intricate are the various combinations thus arising, that no country has as yet produced a map exhibiting all the peculiarities of its soils; and it is probable that the advantage to be derived from such a map would by no means compensate for the expense of constructing it. I shall, therefore, confine myself to making a very few general remarks on the subject.

The soils of Otago, taken as a whole, are decidedly above the average in quality, and this appears to me to be owing to the great extent of mica-schist exposed at the surface, the decomposition of which has supplied more or less directly almost all the soil in the Province.

That this schist contains a considerable amount of lime, is proved by the incrustations of carbonate of lime found in nearly all page 96the caves in it, and the good quality of the soil derived from it is well seen in the Dunstan district, which is remarkably fertile when irrigated.

These mica schist soils occupy nearly the whole of the interior of Otago proper; but those of the Te Anau district and the northern part of Southland are derived from the decomposition of slates and sandstones. Around the east coast, and in the south-western part of Southland, a considerable extent of limestone soil occurs, and this on the east coast is often intermixed with the debris of basaltic rocks; a mixture which, theoretically at least, forms the finest soil in the world. The poorest land is found on the coal fields and on some of the trachytic rocks near Dunedin, but it is limited in quantity.

It is not the quality of the soil, but the mountainous nature of the country, that is the great drawBack to agriculture in Otago, and this acts not only directly in the rocky and precipitous character of large parts of the Province, but also indirectly, by causing all the rivers to be mountain torrents, which have covered with gravel, and utterly spoilt large areas of what would otherwise have been fine alluvial soil. The gold miners are also now in league with the rivers, and we may feel sure that before many years are passed, considerable quantities of agricultural land will be either washed away or covered with "tailings."