"Yes," she assented, and then timidly, "it is 3,213 miles
wide, is it not?"

"Yes," he said, "and 1,781 miles deep! It reaches from
the forty-ninth parallel to the Gulf of Mexico."

"Oh," cried the girl, "what a vivid picture! I seem to
see it."

"Its major axis," he went on, his voice sinking almost
to a caress, "is formed by the Rocky Mountains, which
are practically a prolongation of the Cordilleran Range.
It is drained," he continued--

"How splendid!" said the girl.

"Yes, is it not? It is drained by the Mississippi, by
the St. Lawrence, and--dare I say it?--by the Upper
Colorado."

Somehow his hand had found hers in the half gloaming,
but she did not check him.

"Go on," she said very simply; "I think I ought to hear
it."

"The great central plain of the interior," he continued,
"is formed by a vast alluvial deposit carried down as
silt by the Mississippi. East of this the range of the
Alleghanies, nowhere more than eight thousand feet in