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On Some Tertiary Deposits in South Australia
Rev. Julian Edmund WOODS. Philosophical Magazine, 1860.
The author, in the first place, described the geographical features of that part of the colony of South Australia to which his observations refer. It lies between the River Murray on the west, and the colony of Victoria on the east; and includes an area 156 miles long, N. and S., and 70 broad from E. to W. Some trap-dykes and four volcanic hills are almost the only interruptions to the horizontality of these plains, which rise gradually from the sea, and are occupied by the Tertiary beds to be noticed; they extend into Victoria for some seventy miles, as far as Port Fairy.
In some places on the plains a white compact unfossiliferous limestone lies under the surface-soil; and is sometimes 30 feet thick. Under this is a fossiliferous limestone. The passage between the two is gradual. This latter rock is made up of Bryozoa - perfect and in fragments - with some Pectens, Terebratuloe, Echinoderms, &c.
Sometimes this rock appears like friable chalk, without distinct fossils.. A large natural pit, originating from the infalling of a cave, occurs near the extinct volcano Mount Gambier, and is 90 feet deep - showing a considerable thickness of this Bryozoan deposit in several beds of 14 ft., 10 ft., 12 ft. thickness. Similar pits show the deposit in the same way at the Mosquito Plains, 70 miles north.
Regular layers of flints, usually black, rarely white, occur in these beds, from 14 to 20 feet apart. These, with its colour, and with the superficial sand-pipes, perforating the rock to a great depth, give it a great resemblance to chalk.
The whole district is honeycombed with caves - always, however, in the higher grounds in the undulations of the plains.
One of the caves, in a ridge on the northern side of the Mosquito Plains, is 200 feet long, is divided into three great halls, and has extensive side chambers. The caves have a north and south direction, like that of the ridge. The large cave has a great stalactite in it; and many bones of Marsupialia are heaped up against this on the side facing the entrance ; possibly they may have been washed up against this barrier by an inflowing stream. The dried corpse of a native lies in this, cave. It has been partially entangled in the stalactite; but this man was known to have crept into the cave when he had been wounded, some fourteen years ago. Many of the caves have great pits for their external apertures, and contain much water.
Some shallow caves contain bones of existing Marsupialia, which have evidently been the relics of animals that fell into the grass-hidden aperture at top.
The caves appear in many cases to be connected with a subterranean system of drainage; currents and periodical oscillations being occasionally observed in the waters contained in them. There is but little superficial drainage. One overflowing swamp was found by
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the author to send its water into an underground channel in a ridge of limestone.
Patches of shelly sand occur here and there over the 10,980 square miles of country occupied by the white limestones; but near the coast this shelly sand thickens to 200 feet.
A coarse limestone forms a ridge along the coast-line, and it contains existing species of shells. This indicates an elevation of the coast of late date, and which probably is still taking place.