The Geologist/Volume 5/On the Occurrence of a Peculiar Substance in the Limestone of South Australia
ON THE OCCURRENCE OF A PECULIAR SUBSTANCE IN THE LIMESTONE OF SOUTH AUSTRALIA.
By W. Murray, Esq., C.E.
Fig. 1.
Taking a section across the Murray River Valley, in South Australia, for a distance of about forty miles from west to east, we have (as shown in the accompanying diagram) two parallel ranges, and on the outer flank of the western range there are at some places micaceous strata (A), having a steep inclination, resting against the contorted strata of the range, sections of which are seen in gaps and gullies, with steep sides, in some instances 800 to 1000 feet deep. These hills are partly granitic; the granite is reddish, very readily decomposed, and worn by the rain and weather here and there into strange grotesque figures. There are well-defined metallic lodes in this range. East of these hills are three terraces leading down to the river. The first is the broadest, extending about two-thirds the distance, and falls twenty feet to the river. It is composed chiefly of sand; but rocks similar to those of the western rock crop out here and there. The second terrace averages about two-ninths of the distance between the range and the river: it falls about thirty feet; sometimes not more than ten or fifteen feet; at places, however, more than fifty feet. The third or lowest terrace is only one-ninth of the distance, and nearly level with the river: in fact, it is overflowed when the water is up. The river itself flows slowly, having a fall of about one foot a mile. It is at the fall or escarpment between the second and the third terrace, on an exposed face of friable limestone, that the peculiar substance referred to in this notice is found. The whitish limestone (similar to the bryozoal limestone of the Mount Gambier district) has its exposed edges excavated by innumerable burrows of wallabies, kangaroo-rats, opossums, etc., which live and breed here in countless numbers, far in the body of the rock, and the upper part of the openings of these burrows are coated with a softish-brown fetid material, which appears to be the concreted exhalations and effluvia coming from the heated interiors of these long-inhabited and thickly tenanted burrows. The concretion is thickest just within and at the mouth of a burrow, and dies away upwards on the face of the rock, just as the stain of smoke coming from a crevice is dark at the fissure, and becomes fainter and fainter up the side of the wall. This material is several inches thick, and, owing to the dryness of the climate, is not washed away by rain. In England the specimens brought over are somewhat deliquescent. It has not yet been examined chemically.
Fig. 2.
This curious concomitant of cave-habitats in a warm and dry climate seems worth notice as connected with the subject of bone-caves. The same country (South Australia) is likely to afford valuable information relative to the origin and early condition of subterranean caves and fissures; for the limestone of the Mount Gambier district is extensively excavated by subterranean drainage, on which the water-supply of the towns and stations is, to a large extent, dependent.
The samples of brown material referred to in the above remarks were obtained from a place on the River Murray, near the Reedy Creek (Toongell) or the Thirty-nine Sections, called Pontarra, or Green Corner, and at Cooloodee. It is about fifty miles due-east of Adelaide, and about 35° south latitude, and 139° 20′ east longitude. I found it while making my surveys for the direct eastern line of railway from Adelaide to the River Murray (see Council Paper, No. 47, September 10th, 1858, S. A.).
The River Murray and its tributaries drain an immense district in New South Wales, Victoria, and South Australia, discharging itself into the Lake Alexandria in South Australia; thence to the sea it is navigable for 1500 miles.
[Our readers are referred also to the Journal of the Geological Society, No. 63, August, 1860, pages 252–261, for some account of the geology of the South-Australian district above referred to.—Edit. Geologist.]