"Oh, tell us about it, please," begged Susie. "We'll read about it together," said Uncle Robert, "in the Big Book." "What book?" asked Donald. "The book that lies all around us, which was written by the Creator of the world," said Uncle Robert. "We are reading a page of it now." "Just under the current out there," said Frank, "the bed of the river is covered with all kinds of stones. Some of them are as big as these boulders. I suppose the river brought them down." "What do you think makes the pebbles round?" asked Uncle Robert. "Maybe the river wears off the rough edges," suggested Frank, thoughtfully. "Yes," said Uncle Robert, "the current of the river rolls them over and over on the river bed, and they rub and grind against each other." "What becomes of the stuff that is worn off from them?" asked Frank. "Don't you see it--there?" said Uncle Robert, pointing to the beach. "Oh, you mean the sand," said Donald, taking up a handful and examining it. "Is that the way the nice white sand is made?" asked Susie. "That's what you meant when you said the river worked," said Frank. "Did these boulders come down the river too?" "The story of the boulders," said Uncle Robert, "is different from the story of the pebbles. The water helped grind the pebbles, but it took ice to make the boulders." "Ice!" the children all exclaimed. "Yes, ice. A long, long while ago this land was covered by a great river, or sea of ice, and that was the time these boulders were made," said Uncle Robert. "Can we read about that in the Big Book?" asked Donald. "Some of it," said Uncle Robert. "There are many wonderful stories in this beautiful world--stories more wonderful than any fairy tale. But we must go home now, children; it's getting late." The setting sun threw long shadows of the trees over the river as they rowed home, and the happy day was done. CHAPTER XIII. A RAINY DAY. It was raining, but no one was surprised. They had expected it. The day before had been one of those warm, midsummer days, beginning with a clear sky and a strong south wind. By noon heavy white clouds that looked like heaps of down floated slowly overhead. [Illustration: The weather vane.] The weather vane, which in the morning had pointed to the south, turned from side to side, as though uncertain which direction it liked best. Toward afternoon it seemed to settle the question in favor of the east. The clouds did not rise higher and become thinner and more scattered, as such clouds do if the weather is fair. They kept their white, billowy edges, and rested heavily on straight bands of dull gray. When the sun set, the scroll--like edges of the clouds were tinged with gold and rose color, but under the glittering fringe remained the solid banks of gray and misty purple. The thermometer had been high all day, for it was very warm. The barometer had slowly but surely fallen.