through which the Chain Hills tunnel passes, belong to the Kakanui series, and consist of fine-grained laminated mica-schists and phyllites, passing insensibly into the coarser schists of the underlying Wanaka formation, which is possibly of Devonian age. As no fossils have been found in these rocks, their age can be merely a matter of stratigraphical conjecture. To the north they disappear under the basalts of Flagstaff Hill.
Eruptive Rocks.—The eruptive rocks may justly claim a large share of attention in the consideration of the geological structure of the district we are discussing, as, but for their presence, the features of the country would have been entirely different. It is of the greatest importance, especially in a new country, to have materials for the construction of roads, and for this purpose, the compact basalts are eminently fitted. As settlement progresses, and the prosperity of the inhabitants increases, more substantial building materials are required than the timber which succeeded the wattle-and-dab order of architecture of the early settlers. Hardly any material can surpass as ornamental and durable building stones, the trachytes, breccias, and basalts of our immediate neighbourhood, which may be observed in tasteful combination with various sandstones in most of the public edifices of Dunedin. In the future, when massive stone piers and wharves are required to replace the present wooden structures, as our fine public buildings have replaced the timber and sheet-iron shanties of a few years ago; these natural advantages will enable them to be erected with a maximium of durability and a minimum of cost.
Geologically speaking, the volcanic rocks of the Dunedin basin are of great interest and importance. The main mass of hills between Blueskin and Port Chalmers is composed of trachyte tuff and breccia, intersected with basaltic dykes. The structure of the east end of the Peninsula is very complicated, basalts and trachytes being mixed in the most confusing manner, while apparently underlying both, there is, at Portobello, an extensive development of a rather coarse-textured propylite, composed of greyish-green felspar with crystals of hornblende, etc. Underlying the volcanic series in the locality of Broad Bay, are, as has been already mentioned, sandstones and limestones, belonging to the coal series. The relation of the
