Abstract
AMONG the magazines received by us, the Fortnightly is well to the front as regards articles having a scientific interest. Dr. Alfred R. Wallace writes on “The Ice Age and its Work,” with the object of explaining “the nature and amount of the converging evidence demonstrating the existence of enormous ice-sheets in the northern hemisphere, to serve as a basis for the discussion of the glacial origin of lake-basins, which will form the subject of another article.” After briefly describing the foundation of the science dealing with glaciers and their action, and the early school of glacialists, Dr. Wallace states the phenomena which points to the former existence of glaciers in regions where the mountain-tops are at present below the snow-line. These are classified as follows:—(1) Moraines and drifts; (2) Rounded, smoothed or planed rocks; (3) Striæ, grooves, and furrows on rock-surfaces; (4) Erratic and perched blocks. As a good example of a moraine, that in Cwm Glas, on the north side of Snowdon, is mentioned, together with those in Glen Isla (Forfarshire), and the Troutbeck alley near Windermere. In Cwm Glas, also, smoothed and rounded rocks are to be seen above the moraine. Striated, grooved, and fluted rocks are exemplified by those near the lakes of Llanberis, and by the remarkable effects exhibited at Kelly's Island, at the western end of Lake Erie. The enormous block near St. Petersburg, and the mass of Swedish red granite found at Fürstenwalde, south-east of Berlin, are given as instances of erratic blocks. The erratic blocks from the higher Alps, which are found on the flanks of the Jura Mountains, are also shown to point conclusively to the former existence of glaciers stretching down the Rhone Valley as far as the Jura. The distribution of erratics in North America are next considered, and the crowning example of boulder transportation is said to be afforded by “the blocks of light grey gneiss discovered by Prof. Hitchcock on the summit of Mount Washington, over 6000 feet above sea-level, and identified with Bethlehem gneiss, whose nearest outcrop is at Jefferson, several miles to the north-west, and 3000 or 4000 feet lower than Mount Washington” After giving instances in Great Britain and Scandinavia of boulders carried above their source, Dr. Wallace says:—
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Science in the Magazines. Nature 49, 31–32 (1893). https://doi.org/10.1038/049031d0
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DOI: https://doi.org/10.1038/049031d0