Page:Picturesque Dunedin.djvu/99

Rh Valley is quartzite, no doubt altered from the Caversham sandstones, and in many places halloysite and chloropal, with other decomposition products.

We cannot, in the immediate vicinity of Dunedin, boast of any great natural mineral riches; still the geological features of the district are not of an unfavourable character for the development of a city. There are, it is true, no deposits of true coal, but close to our doors is the excellent fuel from Green Island, known as brown coal, and existing in very large quantities; and on either side the Kaitangata and Shag Point coalfields (see appendix) are ready to supply us with pitch-coal of the highest quality. The coal at Green Island is hydrous brown coal, containing, as will be seen by the following analysis, about 16 per cent. of water:—

(Mean of analyses of Green Island coal recently made in Colonial Laboratory for Railway Department.)

It occurs in a seam 19ft. thick, and has when first got a lustrous appearance and dark brown colour, but on account of the large proportion of water contained, dessicates and crumbles on exposure to the air. It burns freely, with a slightly unpleasant smell, and leaves a bulky incandescent ash; as a fuel for locomotion it does moderately well; and the slack and small coal are largely used for stationary engines. When left below ground the slack is very liable to spontaneous combustion, and many mines have been lost from this cause.

In the coal measures are first-class clays and fire-clays; indeed in the matter of materials for making bricks, the locality is thoroughly well supplied.

An excellent sand for building exists in large quantities in the neighbourhood.

The soil of Dunedin and the environs may be said to be generally of an excellent quality; with the exception of the