It was not dark in this vast cave, yet the light seemed to come from underneath the water, which all around them glowed with an exquisite sapphire color.  Where the little waves crept up the sides of the rocks they shone like brilliant jewels, and every drop of spray seemed a gem fit to deck a queen.  Trot leaned her chin on her hands and her elbows on her lap and gazed at this charming sight with real enjoyment.  Cap’n Bill drew in the oars and let the boat drift where it would while he also sat silently admiring the scene.

Slowly the little craft crept farther and farther into the dim interior of the vast cavern, while its two passengers feasted their eyes on the beauties constantly revealed.  Both the old seaman and the little girl loved the ocean in all its various moods.  To them it was a constant companion and a genial comrade.  If it stormed and raved, they laughed with glee; if it rolled great breakers against the shore, they clapped their hands joyfully; if it lay slumbering at their feet, they petted and caressed it, but always they loved it.

Here was the ocean yet.  It had crept under the dome of overhanging rock to reveal itself crowned with sapphires and dressed in azure gown, revealing in this guise new and unexpected charms.  “Good morning, Mayre,” said a sweet voice.

Trot gave a start and looked around her in wonder.  Just beside her in the water were little eddies—­circles within circles—­such as are caused when anything sinks below the surface.  “Did—­did you hear that, Cap’n Bill?” she whispered solemnly.

Cap’n Bill did not answer.  He was staring with eyes that fairly bulged out at a place behind Trot’s back, and he shook a little, as if trembling from cold.  Trot turned half around, and then she stared, too.  Rising from the blue water was a fair face around which floated a mass of long, blonde hair.  It was a sweet, girlish face with eyes of the same deep blue as the water and red lips whose dainty smile disposed two rows of pearly teeth.  The cheeks were plump and rosy, the brows gracefully penciled, while the chin was rounded and had a pretty dimple in it.

“The most beauti-ful-est in all the world,” murmured Cap’n Bill in a voice of horror, “an’ no one has ever lived to—­to tell the tale!”

There was a peal of merry laughter at this, laughter that rippled and echoed throughout the cavern.  Just at Trot’s side appeared a new face even fairer than the other, with a wealth of brown hair wreathing the lovely features.  And the eyes smiled kindly into those of the child.  “Are you a—­a mermaid?” asked Trot curiously.  She was not a bit afraid.  They seemed both gentle and friendly.

“Yes, dear,” was the soft answer.

“We are all mermaids!” chimed a laughing chorus, and here and there, all about the boat, appeared pretty faces lying just upon the surface of the water.

“Are you part fishes?” asked Trot, greatly pleased by this wonderful sight.