had happened in the building itself, and that was found when he
saw that the deposit-vault had actually risen an inch.

He at once connected the rise in the flooring above the hollow
pile with the pipe in the pile. Estelle had heard liquid sounds.
Evidently water had been forced into the hollow artesian pipe under
an unthinkable pressure when the catastrophe occurred.

From the rumbling and the suddenness of the whole catastrophe
a volcanic or seismic disturbance was evident. The connection of
volcanic or seismic action with a flow of water suggested a geyser or
a hot spring of some sort, probably a spring which had broken through
its normal confines some time before, but whose pressure had been
sufficient to prevent the accident until the failure of its flow.

When the flow ceased the building sank rapidly. For the fact
that this "sinking" was in the fourth direction--the Fourth
Dimension--Arthur had no explanation. He simply knew that in some
mysterious way an outlet for the pressure had developed in that
fashion, and that the tower had followed the spring in its fall
through time.

The sole apparent change in the building had occurred above the
one hollow concrete pile, which seemed to indicate that if access
were to be had to the mysterious, and so far only assumed spring,
it must be through that pile. While the vault retained its abnormal
elevation, Arthur believed that there was still water at an immense
and incalculable pressure in the pipe. He dared not attempt to tap
the pipe until the pressure had abated.