Page:Transactions NZ Institute Volume 10.djvu/59

 Stewart. — Evidences of Change in the Elevation of the Waikato District. 35

If, again, we suppose a bar of harder formation than the rest of the valley to have existed and which had dammed the waters back ; to be reduced by the current, the same kind of changes would take place in the channel above, as we have considered would be effected by the raising of the land, and the amount by which the dam had been lowered would be traceable approximately, in viewing the levels of the old and new channels.

In the lower and middle Waikato, the features of the country indicate that possibly both these causes have contributed to the changes of the position and levels of the river. At Mangatawhiri the river leaves the sandy alluvial flats and takes westward through the Tuakau Gorge to the sea. If we view the country upwards from thence, we can observe some of the more salient features of the scene. And we find on passing each successive gorge through which the river has, in by-gone ages, cut its way, that the banks are higher than they are below, presenting in the higher reaches three, five, and even seven terraces, each indicative of a level for the time being of the river, or lake-like stream, before these natural dams in the gorges were lowered.

The evidence also that at these ancient river levels, the waters found other routes to the sea, nearly amounts to demonstration. So much for the lowering of the river through the formation of the land. Regarding the country having risen, it is, almost equally beyond doubt, that the sea once washed the bases of the inland hills in the Thames and Waikato valleys. In Vol. III. Art. 25, "Trans. N.Z. Inst.," Mr. Kirk gives a list of littoral plants, some of which he found established one hundred miles inland of the present tidal influence. The natural inference that these plants were left in the salt marshes, formerly at the base of the now far inland hills, by the sea which receded as the land arose, supports the opinion expressed by Dr. Hochstetter, and points to a comparatively recent elevation of the land. It seems clear enough, then, that to both erosion of natural dams, and to an elevation of the country, are to be traced the causes of the river now flowing at from ten to more than one hundred feet (speaking well within the mark) lower than it has formerly done. These estimations being from the sea to the Maungatautari Gorge, to which division the present notes are mainly confined.

The speculative thought to which we are invited by these considerations abounds in interest ; but when we find in the midst of alluvial sands, occupying the place where once the ocean rolled, indubitable evidence of the previous subsidence of the whole country, we find the subject increased in complexity, and leading to fields of vast speculative study, which topo- graphers will not soon exhaust. The waters of the river have lowered, or the land has been raised, or both combined. The extent of this we can