About three-fourths of the "inner" surface of the earth is land and about one-fourth water. There are numerous rivers of tremendous size, some flowing in a northerly direction and others southerly. Some of these rivers are thirty miles in width, and it is out of these vast waterways, at the extreme northern and southern parts of the "inside" surface of the earth, in regions where low temperatures are experienced, that fresh-water icebergs are formed.