Glaciers are great sheets of ice, sometimes over a thousand feet thick, which are now known only in Greenland and Antarctica and in high mountains. During several of the glacial periods in the Ice Age, the glaciers covered most of Canada and the northern United States and reached down to southern England and France in Europe. Smaller ice sheets sat like caps on the Rockies, the Alps, and the Himalayas. The continental glaciation only happened north of the equator, however, so remember that “Ice Age” is only half true. As you know, the amount of water on and about the earth does not vary. These large glaciers contained millions of tons of water frozen into ice. Because so much water was frozen and contained in the glaciers, the water level of lakes and oceans was lowered. Flooded areas were drained and appeared as dry land. There were times in the Ice Age when there was no English Channel, so that England was not an island, and a land bridge at the Dardanelles probably divided the Mediterranean from the Black Sea. A very important thing for people living during the time of a glaciation was the region adjacent to the glacier. They could not, of course, live on the ice itself. The questions would be how close could they live to it, and how would they have had to change their way of life to do so. GLACIERS CHANGE THE WEATHER Great sheets of ice change the weather. When the front of a glacier stood at Milwaukee, the weather must have been bitterly cold in Chicago. The climate of the whole world would have been different, and you can see how animals and men would have been forced to move from one place to another in search of food and warmth. On the other hand, it looks as if only a minor proportion of the whole Ice Age was really taken up by times of glaciation. In between came the _interglacial_ periods. During these times the climate around Chicago was as warm as it is now, and sometimes even warmer. It may interest you to know that the last great glacier melted away less than 10,000 years ago. Professor Ernst Antevs thinks we may be living in an interglacial period and that the Ice Age may not be over yet. So if you want to make a killing in real estate for your several hundred times great-grandchildren, you might buy some land in the Arizona desert or the Sahara. We do not yet know just why the glaciers appeared and disappeared, as they did. It surely had something to do with an increase in rainfall and a fall in temperature. It probably also had to do with a general tendency for the land to rise at the beginning of the Pleistocene. We know there was some mountain-building at that time. Hence, rain-bearing winds nourished the rising and cooler uplands with snow. An increase in all three of these factors--if they came together--would only have needed to be slight. But exactly why this happened we do not know.