went, therefore, scrambling up the rocky slope, when, having
reached the rim, we looked down into the little crater. The area of its
floor was only about an acre in extent, but instead of being grown over
with grass and sagebrush, as was the case with most of them, this one
was covered with blocks of stone of all sizes, some of them weighing
several tons. It was evident that the walls, which were only about
thirty feet in height, had at one time been much higher, but that in the
course of ages they had broken down and thus littered the little
bowl-shaped depression with the fragments.

The thread of water which had drawn us up there came trickling out from
among these blocks of stone, and we set out at once to trace it up to
its source while we still had daylight. But this, we found, was by no
means easy, for, though the stream did not dodge about much, but ran
pretty directly down to the crack in the wall, its course was so much
impeded by rocks, under and around which it had to make its way--while
over and around them we had to make _our_ way--that it was ten or
fifteen minutes before we discovered where it came from.

We had expected to find a pool of rain-water, more or less extensive,
seeping through the sand and slowly draining away. What we actually did
find was something very different: something which filled us with wonder
and excitement!

About the middle of the little crater there came boiling out of the
ground a strong spring, which, running along a deep, narrow channel it
had in the course of many centuries worn in the solid stone floor of the
crater, disappeared in turn beneath the litter of rocks. A short
distance below the spring the channel was half filled for some distance
with fragments of stone of no great size, which, checking the rush of
the water, caused it to lap over the edge. It was this slight overflow
which supplied the driblet we had followed up from the canyon below.

"Joe!" I exclaimed, greatly excited. "Do you know what I think?"

"Yes, I do," my companion answered like a flash. "I think so, too. Come
on! Let's find out at once!"

Following the channel, we went clambering over the rocks, which just
here were not quite so plentiful, until, at a distance from the spring
of about fifty yards, we came upon a large circular pool in which the
water flowed continuously round and round as though stirred with a
gigantic spoon, while in the centre it spun round violently, a perfect
little wh