eighted only enough to overcome the actual water pressure, that is,
between the voids of the sand. It seems to the speaker that the only
really safe way is to make the tunnel at least as heavy as the water
displaced in order to prevent it from coming up, and to take other
measures to prevent it from going down. The City of Toronto, Canada,
formerly pumped its water supply through a 6-ft. iron pipe, buried in
the sand under Toronto Bay and then under Toronto Island, with an intake
in the deep water of the lake. During a storm a mass of seaweed, etc.,
was washed against the intake, completely blocking it, and although the
man at the pumping station knew that something was wrong, he continued
to pump until the water was drawn out of the pipe, with the result that
about half a mile of the conduit started to rise and then broke at
several places, thus allowing it to fill with water. Eventually, the
city went down to bed-rock under the Bay for its water tunnel.

Another reason for calling this paper dangerous for beginners is that it
is improbable that experienced engineers or contractors will omit the
bracing at the bottom, although, since the paper was printed, a glaring
instance has occurred where comparatively little bracing was put in the
bottom of a 40-ft. cut, the result being a bad cave-in from the bottom,
although all the top braces remained in place. Most engineers will agree
that nearly every crib which has failed slipped out from the bottom, and
did not turn over.

The objection to the angle of repose is that it is not possible to
ascertain it for any material deposited by Nature. It could probably be
ascertained for a sand bank deposited by Man, but not for an excavation
to be made in the ground, for it is known that nearly all earth, etc.,
has been deposited under great pressure, and is likely to be cemented
together by clay, loam, roots, trees, boulders, etc., and differs in
character every few feet.

A deep vertical cut can often be made, even in New York quicksand, from
which the water has been drawn, and, if not subjected to jars, water,
etc., this material will stand for considerable time and then come down
like an avalanche, killing any one in its way. In such cases very little
bracing would prevent the slide from starting, provided rain, etc., did
not loosen the material.

The author, of course, treats dry and wet materials differently, but
there are very few places where dry material is not likely to