"Oh, there it is!" exclaimed the mermaid. "Come with me. Hold your hands out before you like this and dive down!"
"But where are we going?" again asked Mary Louise as they sank lower and lower in the sea.
"Oh, I forgot," answered the mermaid, turning with a smile to her little companion; "I was so busy looking for the subway entrance that I forgot your question."
"Goodness!" cried Mary Louise. "I didn't know there was a subway in the sea!"
"To be sure," answered the mermaid. "The track lies along the bottom of the ocean. It's not a railroad train we're going to take, but a water train that comes all the way from the Northern seas, sweeping on like a river in the sea. Wait till we get down there. You'll see how fast it goes."
Mary Louise was too astonished to speak.
"The Pullman cars," continued the mermaid, "are icebergs. They come from the North every summer to take a trip South."
"Whew!" shivered Mary Louise. "I think we ar near one now, for I feel quite cold."
Sure enough, she was right, for there close at hand was a great white object.
"All aboard!" shouted a big polar bear. "Watch your step!"