Periodicity of the Fresh-water Lakes of Australia

Abstract

THE fresh-water lakes of Australia, though insignificant in size in comparison with the extent of the country, possess several features of considerable interest to the naturalist. Lake George, which is generally considered the largest sheet of fresh water on the Continent, is only some twenty-three or twenty-four miles in length and seven miles in breadth at the widest part, and even this lake had no existence twenty-four years ago. A bit of swampy ground across which drays could pass, occupied, in 1852, what is now the lowest part of the lake-bottom, and the rest was taken up by squatters and small farmers, who little dreamed, when they settled on the rich alluvial plain, that within a few years they would be hopelessly driven from their homes by the advancing waters. The present lake is situated, at an elevation of about 2,000 feet above the sea, at the lower end of a shallow basin formed by a fork near the southern extremity of the Blue Mountains, and about 150 miles from Sydney. This basin is some forty to fifty miles in length, and from fifteen to twenty miles in breadth, the mountains rising somewhat rapidly to a height of several hundreds of feet on every side except the south. The depth of the water at the present time is only from 25 to 30 feet, which, considering the extent of land submerged, affords a strong argument in favour of the supposition that the lake existed in past times, and was at least as extensive as it is now. An examination of the banks of the creek which rues into the head of the lake confirmed this hypothesis, and led me to believe that it has at one time been much more extensive than it is at present, for the horizontal layers of alluvial deposit could be traced along either hank at an elevation of 10 or 12 feet above trie present lake-surface. This, however, could not have been the case within the last one hundred years—probably not within many hundreds of years—for the present lake is fringed with broad expanses of partially submerged forest trees, that must have attained a growth of more than a century before the waters overtook them. It may, therefore, I think, be assumed that the lake has never in recent times been so extensive as it is now. but that formerly it was much more so.