rvened between that and
preparations for the next--"Mr. Saunders, sir, can you _h_inform me,
sir, 'ow it is that the sea don't freeze at 'ome the same as it does
_h_out 'ere?"

The countenance of the second mate brightened, for he prided himself not
a little on his vast and varied stores of knowledge, and nothing pleased
him so much as to be questioned, particularly on knotty subjects.

"Hem! yes, Mivins, I can tell 'ee that. Ye must know that before fresh
water can freeze on the surface the whole volume of it must be cooled
down to 40 degrees, and _salt_ water must be cooled down to 45 degrees.
Noo, frost requires to be very long continued and very sharp indeed
before it can cool the deep sea from the top to the bottom, and until it
is so cooled it canna freeze."

"Oh!" remarked Mivins, who only half understood the meaning of the
explanation, "'ow very _h_odd. But can you tell me, Mr. Saunders, 'ow it
is that them 'ere _h_icebergs is made? Them's wot I don't comprehend
no'ow."

"Ay," replied Saunders, "there has been many a wiser head than yours,
puzzled for a long time about icebergs. But if ye'll use yer eyes you'll
see how they are formed. Do you see the high cliffs yonder away to the
nor'-east? Weel, there are great masses o' ice that have been formed
against them by the melting and freezing of the snows of many years.
When these become too heavy to stick to the cliffs, they tumble into the
sea and float away as icebergs. But the biggest bergs come from the foot
of glaciers. You know what glaciers are, Mivins?"

"No, sir, I don't."

The second mate sighed. "They are immense accumulations of ice, Mivins,
that have been formed by the freezings and meltings of the snows of
hundreds of years. They cover the mountains of Norway and Switzerland,
and many other places in this world, for miles and miles in extent, and
sometimes they flow down and fill up whole valleys. I once saw one in
Norway that filled up a valley eight miles long, two miles broad, and
seven or eight' hundred feet deep; and that was only a wee bit of it,
for I was told by men who had travelled over it that it covered the
mountains of the interior, and made them a level field of ice, with a
surface like rough, hard snow, for more than twenty miles in extent."

"You don't say so, sir!" said Mivins in surprise. "And don't they
_never_ melt?"

"No, never. What they lose in summer they more than gain in winter.
Moreover, they are always in motion;