This sentiment was not shared by Rex. At the first sight of the huge creatures, Lassie had given a low growl. Rex stood silent, with a stillness that Ross knew to be ominous, and just as the Forecaster finished speaking, with an angry growl, he started off to do battle against the elephants. It was a sight to see him, with his hair bristling, rushing forward to dispute the passage of these huge brutes who dared to approach the vicinity of Lassie and the puppies. Only the sharp commands of Ross availed to bring him back, and throughout breakfast he lay well in advance of the tent, watching, and growling loudly every time the elephants passed, dragging the flat sleds loaded with sand bags to the cave-in a few hundred yards beyond. "I've been wondering," began Anton, using the expression most often on his lips, "why there are so many floods on the Mississippi. Why is it? Lots of rivers I know don't have these awful floods every year." "I've wondered, too," said Ross. The Weather Man looked at the two boys, then took a cigar out of his pocket. "I can't stay away from the levee very long," he said, "but I need a cigar after breakfast, anyway, and I'll tell you why the Mississippi is one of the worst flood rivers in the world and why the safeguarding of the Mississippi is the biggest piece of work to be done in the United States. It's a bigger piece of work than the Panama Canal, and a more difficult piece of work. It means millions of dollars every year to the people of the United States." "Why is it such a hard job?" "The Mississippi River," the Forecaster began, "is two and a half thousand miles in length; the longest river in the world." "Longer than the Amazon?" asked Anton. "Yes, a great deal. Besides, it is navigable for nearly two thousand miles, clear from St. Paul, Minnesota, to the Gulf. It drains two-fifths of the area of the United States. To put it another way, all the rain and snow that falls between New York State and Montana sooner or later makes its way into the Mississippi River, except for the rain that is used up by plants and animals or that is evaporated before it reaches the river or that drains by underground seepage to the ocean. So you see what a vast amount of water it must carry. Now, boys," he continued, "what kind of banks has the river around here, rock or earth?" "Mud!" answered Ross, tersely. "Right," the Forecaster agreed, "and it is mud nearly all the way along. But do you know what mud is?" This was rather a poser, but finally Anton said slowly, "It's a mixture of earth and water, isn't it?" The Forecaster looked shrewdly at the boy.