Читать книгу The Romance of Modern Geology. Describing in simple but exact language the making of the earth with some account of prehistoric animal life онлайн

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These erratic blocks, now found all over Europe, tell us a good deal about the ice on which they were transported. The blocks that fall on the edges of the glacier remain on the side where they descend. Hence, if there is any notable difference in the composition of the rocks on either side of the valley, the existence of this difference will be preserved in the moraines. If, therefore, in a country where the glaciers have disappeared we can trace the scattered blocks up to their sources among the mountains, we can say what was the track followed by the prehistoric glaciers. In Europe there are several examples of the uses of this detective evidence. Thus the peculiar blocks of the Valais mountains can be traced right on to Lyons; and this shows us that the glacier from which the River Rhone sprang extended once right across the east of France to Lyons, and probably farther. It was therefore once at least 170 miles longer. Similarly, blocks which are exactly like the characteristic rocks peculiar to Southern Scandinavia are found in Northern Germany, Belgium, and East Anglia; and we therefore believe that a great sheet of ice once filled up the Baltic and the German Ocean, carrying with it immense numbers of northern "erratics." In our own country, in fact, glacier boulders are found in nearly every county, and show that once the greater part of the country was buried under ice.