en if we had to take up
our search for intelligent life later.

We remarked that none of these enormous structures were square, or with
right-angled corners, such as we were used to. They all seemed to be a
combination or multiplication of a single design, which was nothing more
than a massive triangular wall, with its right angle on the ground and
its acute angle at the top. Sometimes two were built together, with
their perpendicular surfaces joining; again, four were joined in the
same manner, and one very large one was composed of twelve of these,
radiating from a common centre, which, if they had quite joined each
other, would have formed a gigantic cone.

I took another look at the tall, slender birds down the river, and
remarked to the doctor,--

"These great structures are no birds' nests! You can't make me believe
winged men would build with stone. These look more like giants'
playthings than anything else."

"They appear to me like the gnomons of enormous sundials," remarked the
doctor; "and, indeed, their uses must certainly be astronomical. With
these one can not only tell the time, but the ascension and meridian of
the sun and stars, and therefore the months and seasons."

We lowered and circled about above the largest one, which had twelve of
the triangular walls built in circular form, with their common
perpendicular line in the centre and their acute angles at the
circumference. On closer observation, the twelve slanting sides, which
radiated from the common peak, had a tubular appearance, and we were
soon able to look down through almost a hundred great cylindrical
chambers, which ran from a common opening at the top, slanting at every
different angle down to the surface.

"These are nothing more than great, immovable masonry telescopes, for
watching the stars in their courses!" cried the doctor. "Look, there is
one perpendicular cylinder for observing just when a star or planet
comes directly overhead, and these scores of other cylinders, at
different angles, successively afford a view of a given constellation as
it rises and then declines."

"Then they have built a separate masonry telescope, pointing in almost
every conceivable direction, instead of having one movable telescope to
take any direction," said I.

The wonderful size and massive construction of these was very striking,
rivalling the pyramids of Egypt in their ponderous and enduring
character. They were located on a raised plateau