Page:Popular Science Monthly Volume 37.djvu/113

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T the recent meeting of the British Association at Newcastle, Prof. James Geikie opened the Section of Geology with a summary of the results obtained during the last few years by continental glacialists. Sketching the steps by which the iceberg theory has been abandoned by German and Swiss geologists, he dwelt on certain features of the drifts of the peripheral areas, which for some time were hard to account for by land-ice. Of these, the bedded deposits occurring so frequently in the bowlder-clays of the peripheral regions, and the occasional silty and uncompressed character of the clays themselves, remained unexplained until a clew was found to their origin in the geographical distribution of the clays in which they occur. These stony clays, of inconsiderable thickness in Norway, the higher parts of Sweden, and in Finland, reach a thickness of about forty-three metres in southern Sweden, and eighty metres in the northern parts of Prussia; and in Holstein attain a depth of one hundred and twenty to one hundred and forty metres, and still greater depths in Hanover, Mark Brandenburg, and Saxony. The aqueous deposits associated with the stony clays also gradually acquire more importance as they are followed from the mountainous and high-lying tracts to the low ground, until, along the southern margin of the drift area, the "diluvium" appears to consist of aqueous accumulations alone. The explanations of these facts by German geologists have been summed up recently (1884) by Dr. Jentzsch, from whom Prof. Geikie quoted enough to show that they are quite in accordance with the views long held by glacialists elsewhere.

The general conclusions reached by continental glacialists, and summarized by Prof. Geikie, are:

1. Before the invasion of northern Germany by the inland ice, the low grounds bordering on the Baltic were overflowed by a sea which contained a boreal and arctic fauna.

2. The next geological horizon in ascending order is that which is marked by the glacial and fluvio-glacial detritus of the great ice-sheet which flowed to the foot of the Harz Mountains, and has been traced by the occasional presence of rock-striæ and roches-moutonnées, of bowlder-clay and northern erratics, rather than by recognizable terminal moraines.

3. A well-marked temperate fauna and flora marks the inter-glacial beds which follow, and which, in their geographical distribution and the presence in them of such forms as Elephas antiquus, Cervus elephas, and C. megaceros, and a flora