slabs and dried or pressed into bricks by machinery.

When vegetation decays in open air the carbon of its tissues,
taken from the atmosphere by the leaves, is oxidized and returned
to it in its original form of carbon dioxide. But decomposing in
the presence of water, as in a bog, where the oxygen of the air is
excluded, the carbonaceous matter of plants accumulates in
deposits of peat.

Peat bogs are numerous in regions lately abandoned by glacier ice,
where river systems are so immature that the initial depressions
left in the sheet of drift spread over the country have not yet
been drained. One tenth of the surface of Ireland is said to be
covered with peat, and small bogs abound in the drift-covered area
of New England and the states lying as far west as the Missouri
River. In Massachusetts alone it has been reckoned that there are
fifteen billion cubic feet of peat, the largest bog occupying
several thousand acres.

Much larger swamps occur on the young coastal plain of the
Atlantic from New Jersey to Florida. The Dismal Swamp, for
example, in Virginia and North Carolina is forty miles across. It
is covered with a dense growth of water-loving trees such as the
cypress and black gum. The center of the swamp is occupied by Lake
Drummond, a shallow lake seven miles in diameter, with banks of
pure-peat, and still narrowing from the encroachment of vegetation
along its borders.

SALT LAKES. In arid climates a lake rarely receives sufficient
inflow to enable it to rise to the basin rim and find an outlet.