“Come, Paul,” said Trove, as he lifted the small boy; “here’s a castle of King Frost.  There are thousands in his family, and he’s many castles.  Building new ones every day somewhere.  Goes north in the spring, and when he moves out they begin to rot and tumble.”

He cleared a space for the boy to stand upon.  Then he brushed away the snow blanket flung loosely over the vault of ice.  A wonderful bit of masonry stood exposed.  Near its centre were two columns, large and rugose, each tapering to a capital and cornice.  Between them was a deep lattice of crystal.  Some bars were clear, some yellow as amber, and all were powdered over with snow, ivory-white.  Under its upper part they could see a grille of frostwork, close-wrought, glistening, and white.  It was the inner gate of the castle, and each ray of light, before entering, had to pay a toll of its warmth.  On either side was a rough wall of ice, with here and there a barred window.  The snow cleared away, they could hear the song of falling water.  The teacher put his ear to the ice wall.  Then he called the boy.

“Listen,” said he; “it’s the castle bell.”  Indeed, the whole structure rang like a bell, if one put his ear down to hear it.

“See!” said he, presently, stirring a heap of tiny crystals in his palm.  “Here are the bricks he builds with, and the water of the brook is his mortar.”

Near the bank was an opening partly covered with snow.  It led to a cavern behind the ice curtain under the rock floor of the brook above.

The teacher took off his snow-shoes.  In a moment they had crawled through and were crouching on a frosty bed of pebbles.  A warm glow lit the long curtain of ice.  Beams of sunlight fell through windows oddly mullioned with icicles and filtered in at the lattice of crystal.  They jewelled the grille of frostwork and flung a sprinkle of gold on the falling water.  The breath of the waterfall, rising out of bubbles, filled its castle with the very wine of life.  The narrow hall rang with its music.

“See the splendour of a king’s home,” said the teacher, his eyes brimming.

The boy, young as he was, had seen and felt the beauty and mystery of the place, and never forgot it.

“See how it sifts the sunlight to take the warmth out of it,” the teacher continued.  “Warmth is poison to the King, and every ray of light is twisted and turned upside down to see if he has any in his pocket.”

They could now hear a loud baying on the hill above.

As they turned to listen, a young fox leaped in at the hole and, as he saw them, checked a foot in the air.  He was panting, his tongue out, and blood was dripping from his long fur at the shoulder.  He turned, stilling his breath a little as the hounds came near.  Then he trembled,—­a pitiful sight,—­for he was near spent and between two perils.

“Come—­poor fellow!” said the teacher, stroking him gently.