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The Pamphlet Collection of Sir Robert Stout: Volume 68

Geology and Topography

Geology and Topography.

The Canterbury Plains are half-moon shaped; some 120 miles long and with a greatest breadth of about 40 miles. Near the middle of the flat, or eastern side, is the cluster of volcanic hills called Bank's Peninsula. These were a group of volcanoes very many ages ago, and all signs of craters have long since been obliterated. They were active when the western islands of Scotland were also pouring out streams of lava. The curved side of the plains is bordered by high mountains to the west, but on the north and south by undulsting hills, which are, however, broken in places by high ridges too steep to plough. The plains themselves slope from the sea up to a level of about a thousand feet under the foot of the western mountains. These western mountains, as well as the high ridges that run from page 15 them on the north and south of the plains, are formed of sandstones and slates of considerable age, dating probably from the carboniferous and jurassic periods, and contain limestone but rarely. But fringing the western side of the plain as well as covering the spurs from the ridges north and south are many different kinds of much younger rocks which afford a great variety of soils and many useful minerals.

Limestones—all of them good for burning and some for building—occur from the Hurunui in the north through the Weka-pass district to Oxford, where there is a deposit of chalk. They are also found in the Malvern Hills, and again in the south near Mt. Somers, Hakahu, like Opihi and Tangawai rivers, and in the Valley of the Waihao.

Brown coals are found at the Malvern Hills, Mt. Somers, Kakahu, and Waihao, while at the Acheron, a tributary of the Rakaia, there is very good anthracite. Good pottery clays generally accompany the coal beds.

Volcanic rocks are by no means rare. Bank's Peninsula is entirely composed of basalts and andesites which decompose into valuable soils. The Malvern Hills also contains both basalts and andesites, although host of its volcanic rocks are rhyolite, which makes a comparatively poor soil; and it is the same with Mt. Somers and the Gawlar Downs. However, at Geraldine and Timaru, we again find basalts, which readily decompose.

The plains themselves are shingly near the great rivers, especially along their northern banks, bat generally the shingle is covered by a layer of silt, which towards the coast passes into rich black soil.

Much of the lower part of Bank's Peninsula, as well as the Mt. Grey and Moeraki Downs, the lower parts of the Malvern Hills and the country between Timaru and the Waitaki river is covered by a silt deposit, often of great depth, forming a loam which would make an almost perfect soil if a little lime were added; and as limestone and coal are both plentiful in many places, the cost of burning and distributing it would not be very great.