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The drought culminating in 1967-68 opened water-traps in Murray Cave, thus permitting the re-exploration and survey in January 1968, of a further 1,000 feet of the main passage. Previous explorations, of which oral tradition persisted, are known to have taken place in 1902-3 and some details of the early visitors are presented. The characteristics of the extension are predominantly shallow phreatic in nature and about half of it episodically functioning in this way at the present time; the water-traps along it are inverted siphons in the strict sense and located at the sharpest changes in cave direction. The exploration limit consists of a rockfall beneath a doline, which appears, therefore, to be at least in part a collapse doline. Beneath two other dolines the cave has no sign of collapse, though tall avens reach towards the surface; these dolines are due to surface solution only. The forward part of the cave is overlain by a short, steep dry valley; the relationship between the two remains problematic but there is good reason not to regard the dry valley as the determinant of the cave's location. The evidence is now stronger for an earlier hypothesis that the cave was formerly the outflow cave of nearby River Cave, a perennially active stream cave. It also seems likely that the episodic activity of Murray Cave is due to flood overflow from River Cave. The hydrological regime of the cave is compared with precipitation records of the nearby stations. The episodic flow through the cave does not require an abnormally wet winter; it can follow fairly quickly after complete emptying of the water-traps and approaches an annual event. Draining of the water-traps is a much less frequent event, but whether a series of low rainfall years is necessary, or a single pronouncedly dry year is sufficient to achieve this, cannot be determined from available data. On either count, it seems probable that the cave opened up two or more times between the known occasions of 1902-3 and 1968 in the period 1909-53 when the cave was visited infrequently.
Mullamullang Cave N37 is the longest and most complex cave on the Nullarbor Plain, Southern Australia. Unlike the other caves, it possesses extensive levels of phreatic solution tube passages which permit stronger inferences to be made on the development of the collapse passages constituting the bulk of Mullamullang Cave and other deep Nullarbor caves. These passages have been formed by collapse through overlying belts of solution tube networks along an elongated zone of cavitation in the limestone. Massive breakdown was probably initiated at depth within the zone, at least 50 feet below the present watertable level. Upward stoping of the collapse would have been facilitated by the higher network levels in the zone, such as the Ezam and Easter Extension. Channelling of groundwater flow under the Plain is suggested by the belt-like nature of the networks. An epiphreatic origin is proposed for the network levels though convincing morphological evidence is wanting. Eustatic changes in sea level have been of fundamental importance in the development of the multiple levels. Wetter periods in the past were probably important as little development is taking place under present-day dry conditions. Correlation of wetter periods with Pleistocene glacials would help explain the development of huge collapse passages, but such correlatien cannot be assumed on present evidence. Massive collapse and doline formation were followed by subaerial weathering and vadose activity which modified the cave - especially near the entrance. Correlation of levels in Mullamullang with those in other Nullarbor deep caves is attempted. However, Mullamullang Cave is unique probably due to the lithology of the Abrakurrie Limestone in which it is developed.
The Nullarbor Plain is a low plateau of Tertiary limestone covering an area of 194,175 km2 in southern Australia. It has a semi-arid climate and supports a stunted vegetation. Ninety-five species of arthropods have been recorded from 47 Nullarbor caves, and many of these species are widely distributed across the Plain. Two possible explanations for their distribution are discussed. Subterranean migration may occur through the widespread zone of small interconnecting cavities in the Nullarbor Limestone, but this has not yet been confirmed. While cave arthropods are confined to the cool, moist cave environment during the day, they have been observed at night in cave entrances, in dolines and on the surface of the Plain. Cave "breathing", similarity in cave and epigean climate at night, strong winds, occasional heavy rain and numerous animal burrows all contribute towards favourable conditions for surface migration.
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