experience to be human skulls. He could
not but marvel as to where so many countless thousands of the things
had come from, until he paused to consider that the infancy of Caspak
dated doubtlessly back into remote ages, far beyond what the outer
world considered the beginning of earthly time. For all these eons the
Wieroos might have been collecting human skulls from their enemies and
their own dead--enough to have built an entire city of them.

Feeling his way along the narrow ledge, Bradley came presently to a
blank wall that stretched out over the water swirling beneath him, as
far as he could reach. Stooping, he groped about with one hand,
reaching down toward the surface of the water, and discovered that the
bottom of the wall arched above the stream. How much space there was
between the water and the arch he could not tell, nor how deep the
former. There was only one way in which he might learn these things,
and that was to lower himself into the stream. For only an instant he
hesitated weighing his chances. Behind him lay almost certainly the
horrid fate of An-Tak; before him nothing worse than a comparatively
painless death by drowning. Holding his haversack above his head with
one hand he lowered his feet slowly over the edge of the narrow
platform. Almost immediately he felt the swirling of cold water about
his ankles, and then with a silent prayer he let himself drop gently
into the stream.

Great was Bradley's relief when he found the water no more than waist
deep and beneath his feet a firm, gravel bottom. Feeling his way
cautiously he moved downward with the current, which was not so strong
as he had imagined from the noise of the running water.

Beneath the first arch he made his way, following the winding
curvatures of the right-hand wall. After a few yards of progress his
hand came suddenly in contact with a slimy thing clinging to the
wall--a thing that hissed and scuttled out of reach. What it was, the
man could not know; but almost instantly there was a splash in the
water just ahead of him and then another.

On he went, passing beneath other arches at varying distances, and
always in utter darkness. Unseen denizens of this great sewer,
disturbed by the intruder, splashed into the water ahead of him and
wriggled away. Time and again his hand touched them and never for an
instant could he be sure that at the next step some gruesome thing
might not attack him. He had strapped his hav