ages, but the exploration of caves in North America has so far failed
to reveal traces of different degrees of civilization.




CHAPTER IX

GREAT TUNNELS OF THE WORLD

Primitive Tunneling--Hoosac Tunnel--Croton Aqueduct--Great Alpine
Tunnels--New York Subway--McAdoo Tunnels--How Tunnels are Built.


The art of tunnel construction ranks among the very oldest in the
world, if not the oldest, for almost from the beginning of his advent
on the earth man has been tunneling and boring and making holes in the
ground. Even in pre-historic time, the ages of which we have neither
record nor tradition, primitive man scooped out for himself hollows
in the sides of hills, and mountains, as is evidenced by geological
formations and by the fossils that have been unearthed. The forming
of these hollows and holes was no indication of a superior intelligence
but merely manifested the instincts of nature in seeking protection
from the fury of the elements and safety from hostile forces such as
the onslaughts of the wild and terrible beasts that then existed on
the earth.

The Cave Dwellers were real tunnelers, inasmuch as in construction of
their rude dwellings they divided them into several compartments and
in most cases chose the base of hills for their operations, boring