The two little ones were making a sand city. They made a square wall of sand, and inside this they built sand houses, railroads, a tunnel and many other things, until Freddie suddenly said:
"Oh, if we only had some of the clam shells that are down by the lake we could make a lot more things."
"So we could!" cried Flossie. "Let's go and get some!"
So, never thinking to ask their father, who was still reading, away rushed the two twins, after "clam" shells. They were not really shells of clams, but of fresh water mussels, but they were almost like the shells of the soft clams one sees at the beach. The mussels are brought up on shore by muskrats who eat the inside meat and leave the empty shells. The small twins often used the shells in their play and games.
The place where the mussel shells were usually to be found was not far from the tents, but like most children in going to one place Flossie and Freddie took the longest way. They were in no hurry, the sun was shining brightly, and it was such fun to wander along over the island. So, before they knew it, they were a long distance from "home," as they called Twin Camp.
"Maybe we oughtn't to've come," said Flossie, as she stopped to pick some blueberries.
"We're not so far," said Freddie. "I know my way back. Oh, Flossie! look at that butterfly!" he suddenly called, making a grab for the fluttering creature. The butterfly flew on a little way and Freddie raced after it, followed by Flossie.
"Now I'm goin' to get it!" the little boy cried. With his hat he made a swoop for the butterfly, and then suddenly he and Flossie, who was close behind him, tumbled down through a hole in the ground, which seemed quickly to open at their very feet, between two clumps of bushes.
"Oh!" cried Freddie, as he felt himself falling down.
"Oh, dear!" echoed Flossie.