The thunder-clouds thickened until the whole sky was black; the tide rose in great waves, and the children were glad to be in the house. But the storm played so many strange pranks that they could not keep away from the windows, asking a hundred questions about things that cannot be put in a bird book. "If the water keeps up on end, as it is doing now," said Olaf, "it will be a week before I dare take you over to Gull Island; but I was talking to a man from up the river yesterday, and he says the reed shallows are full of Rails--maybe you'd like to see them." "Rails, what are they?" asked Nat. "I thought rails were the steel things that cars run on, or else some kind of fence bars." "The Rails that Olaf speaks of are marsh birds," said the Doctor. "Some are about as big as Robins, and some are bigger still, shaped like long-legged, long-necked, bob-tailed Hens, with long curved beaks. In fact, some members of the family are called Marsh Hens from this resemblance. Olaf often guides gunners through the waterways to find these birds; he shall take you also, and perhaps you may find some old Marsh Wrens' nests at the same time." The next morning was clear and warm, and the children tumbled out in their flannel bathing-suits to have a dip before breakfast. Rap, by rolling over and over on the sand, was in the water as soon as Nat; but they did not venture out far, even though the tide was low, contenting themselves by splashing about in shallow places. [Illustration: Turnstone.] Presently Nat spied something on the stony end of the bar that stretched out at the right of the beach, and pointed it out to Rap, who said: "They are some sort of birds: you had better get the glass, for even if we could go nearer to them, they would be sure to see us and skip." Then Nat brought the glass and they each took a peep. "The bodies are like speckled Pullets', but the heads are like Pigeons' and the legs are very thin," said Rap. "See! there is a different one, ever so much nearer over on this side, but I can't make him out very well. Here comes the Doctor, all ready to go in swimming; of course he can tell us." "Those mottled birds with red legs are Turnstones," said the Doctor, after looking a moment. "They are wading shore birds, who run about the rock bars and sandy beaches, turning over small stones for the food that is hidden underneath. They very seldom come into bays like this, but keep more on the outer beaches. The other one, with black under parts and dark back finely speckled with yellow, is the Golden Plover, who often visits our beaches and marshy meadows." "Do either of them ever nest up the river?" asked Dodo. "No, indeed--you would have to travel many hundreds of miles to find the lonely Arctic beaches they both call home. They only come this way before they take the long fall journey to South America, where they winter; and in the spring-time they are usually in too great a hurry to stop."