would be the signal of their destruction. It would cut its channel over
the ridge of the lofty mountain, tiny at first, but deepening and
widening with each successive shower, until, after many years--ages,
centuries, cycles perhaps--a great gap such as this," (here Seguin
pointed to the canon), "and the dry plain behind it, would alone exist
to puzzle the geologist."

"And you think that the plains lying among the Andes and the Rocky
Mountains are the dry beds of seas?"

"I doubt it not; seas formed after the upheaval of the ridges that
barred them in, formed by rains from the ocean, at first shallow, then
deepening, until they had risen to the level of their mountain barriers;
and, as I have described, cut their way back again to the ocean."

"But does not one of these seas still exist?"

"The Great Salt Lake? It does. It lies north-west of us. Not only
one, but a system of lakes, springs, and rivers, both salt and fresh;
and these have no outlet to the ocean. They are barred in by highlands
and mountains, of themselves forming a complete geographical system."

"Does not that destroy your theory?"

"No. The basin in which this phenomenon exists is on a lower level than
most of the desert plateaux. Its evaporating power is equal to the
influx of its own rivers, and consequently neutralises their effect;
that is to say, in its exchange of vapour with the ocean, it gives as
much as it receives. This arises, not so much from its low elevation as
from the peculiar dip of the mountains that guide the waters into its
bosom. Place it in a colder position, _ceteris paribus_, and in time it
would cut the canal for its own drainage. So with the Caspian Sea, the
Aral, and the Dead Sea. No, my friend, the existence of the Salt Lake
supports my theory. Around its shores lies a fertile country, fertile
from the quick returns of its own waters moistening it with rain. It
exists only to a limited extent, and cannot influence the whole region
of the desert, which lies parched and sterile, on account of its great
distance from the ocean."

"But does not the vapour rising from the ocean float over the desert?"

"It does, as I have said, to some extent, else there would be no rain
here. Sometimes by extraordinary causes, such as high winds, it is
carried into the heart of the continent in large masses. Then we have
storms, and fearful ones too. But, generally, it is only the skirt of a
cloud, so to speak, that reac