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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Suppose, then, a period when there was very much more snow in winter than now. As the snow accumulated layer on layer the lower part would become squeezed into a mass half ice, half snow; and it is quite likely that the heat of the summer sun (especially if, as we have supposed, the atmosphere was much cloudier then than now) would be unable to dissolve it. Thus the snow age would gradually merge into an ice age, and we can imagine a period when a great deal of Europe was covered with snow or ice as Greenland is to-day. What records would it leave behind? Now, on slopes the sheet of snow would tend to slip just as it slips from sloping house-roofs. In doing so it would push before it any loose material which lay in front of it; and trees or bushes, stone or soil, would be gradually pushed downhill. If the slopes were steep enough the snow-sheets would occasionally break off and sweep down as avalanches. Sometimes these great masses are many thousands of square yards in area and fifty feet thick, and in the late winter and early spring often do immense damage, carrying away houses, trees, and great masses of rocks in their progress. They leave their imprint not only in ground swept bare, but in huge mounds of debris piled up in the valleys below.