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This study assesses human impact on the landscape around Cobrico, a volcanic crater lake in dairying country in south‐western Victoria. It compares the last 150 years of impact of European settlement against approximately the previous 1500 years of prehistoric occupation and land use. Focus is on vegetation dynamics, erosion, productivity changes and the fire regime. Since European settlement there has been woodland clearance and recovery, the introduction of many plant and animal species and a significant increase in the intensity in the fire regime. While many direct linkages are apparent between environmental variables some operate over significant time lags. Fire has played a major role in vegetation dynamics and has favoured open ground taxa at the expense of Eucalyptus and Melaleuca. While major fires do not always lead to erosion in the catchment it is clear that some changes in the chemistry of erosion products have resulted, with potassium and iron showing increases in the historic period.

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Blue solutions and blue solids obtained from the reactions between iodine and antimony pentafluoride, and between iodine, iodine pentafluoride, and antimony pentafluoride, have been studied by chemical, spectroscopic, and magnetic techniques. Similar solutions are formed by iodine in the presence of iodine pentafluoride and the pentafluorides of P. As. Nb, and Ta, but only in the case of Ta is a stable solid isolated. The results are discussed in terms of the iodine molecule cation, 12+.THE anticipation that halogen cations, hal+, should be paramagnetic, was followed by the discovery that a blue species, formed from iodine and iodine monochloride under conditions that should favour the formation of I+, was indeed strongly paramagnetic. This led to an identification1 which appeared to be supported by a variety of measurement^.^^^ Other explanations were discussed, and the possibility that I,+ was responsible was considered. The latter in particular was rejected one one ground; that the formation did not accord with some conductivity data.l However, the more recent discovery that the blue species could be formed in solvents very different from the original sulphuric acid and oleums, and that the absorption bands in the visible region 3-5 were almost completely unaffected by the change, threw considerable doubt on the I+ theory. This required the visible bands to be due to p-9 transitions, depending upon an asymmetric solvation for a ' crystal-field ' splitting3After the present studies were well advanced both in Melbourne and Leicester, Gillespie and Milne published data for solutioss in fluorosulphuric acid which show conclusively that the blue species is not I+. Their results are, however, in good accord with the formulation 12+. They have also extended earlier observations 6,7 and have confirmed the presence of the cations Isf, I,+, and IO+ in strongly acidic media. Their evidence, both for I,+ and the other cations, rests largely on careful R.