d as salt as the tear itself. The lymph
that constitutes the "water" of a so-called "water blister" is also
salty, and even the little blood one gets into his mouth in trying
nature's method of stanching the flow from a cut finger gives the
impression that it contains a little salt. Every fluid of the body is
salty, and every cell of the body is bathed in salt water. It is too
long since the ancestors of our cells swam in the seas of the Eozoic
time for us to assert with any positiveness that the ancestral habit
is responsible for this trait in the descendants. Sure it is that
to-day our cells, like their ancestors of old, live in water, and this
water is slightly salty--as were probably the Archaean seas.

The geologist tries as best he may to build up the geography of the
earth in the past. He endeavors to judge from the rocks as he now
finds them, where the seas, the bays, the dry land, and the mountains
of earlier geological times lay. The present aspect of the earth is
very recent, and earlier ages must have shown an entirely different
distribution of land and water. The North American continent was
certainly very much smaller than it is now. The first known lands lay
close to the Atlantic seaboard and probably extended out into the
water some distance beyond the present shoreline. The stretch of
continent was narrow, and grew narrower as it went southward. In what
is now the Canadian district, a considerable expanse probably existed
in very early times. Then a great internal sea, shallower than the
Atlantic, stretched its unbroken sheet over almost the entire area now
occupied by the United States, while only a comparatively small hump
of earth, ending in a narrower strip, lay where the great Western
plateau now rears its enormous bulk.

A large portion of the history of the North American continent, with
its developing animals and plants, is tied up with the gradual
shrinkage of this interior sea. Slowly across the Canadian district,
the Eastern and Western lands became connected with each other, while
the waters progressively were pushed down the continent, which was
steadily growing from the east and from the north, though less slowly
from the west, into this internal sea. To-day only the Gulf of Mexico
remains as evidence of the broad stretch that once extended through to
the Arctic Ocean and west beyond the present position of the Rocky
Mountains.

How this great Eastern backbone of the continent was produ