Detection of anomalies in measurements of low rates of limestone surface lowering with a traversing micro-erosion meter (MEM) led to temperaturecontrolled laboratory and field investigations of some sources of error in the method. Regressions for the correction of temperature change in the instrument and in the stud-rock interface were obtained. Probe erosion tests permitted a correction to be devised and also provided information whereby a measure of operational irregularity was adopted. Corrections and error terms were applied to field measurements from two southern New South Wales karsts and a collection of Australian limestone slabs exposed at one site.Examination of these results and of published MEM rates from other parts of the world validated the MEM method. Marine platforms are lowered at such gross rates that these error sources may be neglected there. However limestone lowering in terrestrial environments cannot be assumed to proceed at rates which permit this and recommendations are made about procedures to ensure that investigations are prosecuted within the limitations of the method.

A traversing microerosion meter (MEM) was used to measure the rates of surface weathering of limestones in southeastern Australia. There were two groups of MEM sites installed in 1978/9. The aim of the experimental design for the first type, the 13 sites at Cooleman Plain and Yarrangobilly Caves, was to obtain erosion rates for limestones of similar lithology exposed under comparable climate conditions. The sites were positioned to measure erosion over a range of microsolutional forms and with exposure to differing forms of erosion, i.e. subaerial, subsoil and instream. The second set, at Ginninderra close to Canberra, consists of nine limestone slabs of differing lithology, collected from different locations but exposed under identical climatic conditions. The number of individual measurement points at each MEM site varied from 24 to 68.There were major differences in erosion rates between subaerial bedrock and instream sites at Yarrangobilly and Cooleman Plain, but no evidence of differential erosion across the micro-forms. There were differences in the weathering rate for bedrock sites, due to climatic differences, and between the limestone lithologies exposed at Ginninderra. The average rate of erosion for the subaerial bedrock sites at Cooleman Plain and Yarrangobilly over the 13 years was 0.01 3 mm a-' and at Ginninderra 0.006 mm a-' . At some of the sites microflora (lichens and mosses) caused problems for field measurement.The weathering processes that contribute to the surface lowering are discussed in the accompanying paper by Moses et al.

Results from long term microerosion meter (MEM) studies indicate that microenvironments are characterized by different erosion rates. A complementary study, carried out on the same sites, examines the microscale morphology in each environment. Optical and scanning electron microscopy were used to identify a range of features thought to reflect different processes.Under subaerial conditions micromorphology is dominated by biological weathering features owing to the presence of microflora. Sites permanently covered by soil or stream water have only dissolution etch features, though stream sites may exhibit microfractures. Sites with periodic exposure exhibit both dissolution and biological etch features. The natural environment is more accurately reflected by allowing some microflora colonization of MEM sites rather than preventing colonization by artificial means.KEY WORDS limestone weathering; biological erosion; microerosion meter; optical and scanning electron microscopy; micromorphology

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