The vast unexplored regions of Africa, South
America, and Central Australia, may yet yield further clues, and
the riddle of insect-metamorphosis may some day betray the
secrets which it must hold. For the moment the Carboniferous
insects interest us as a rich material for the operation of a
coming natural selection. On them, as on all other Carboniferous
life, a great trial is about to fall. A very small proportion of
them will survive that trial, and they trill be the better
organised to maintain themselves and rear their young in the new
earth.
The remaining land-life of the Coal-forest is confined to
worm-like organisms whose remains are not preserved, and
land-snails which do not call for further discussion. We may, in
conclusion, glance at the progress of life in the waters. Apart
from the appearance of the great fishes and Crustacea, the
Carboniferous period was one of great stimulation to aquatic
life. Constant changes were taking place in the level and the
distribution of land and water. The aspect of our coal seams
to-day, alternating between thick layers of sand and mud, shows a
remarkable oscillation of the land. Many recent authorities have
questioned whether the trees grew on the sites where we find them
to-day, and were not rather washed down into the lagoons and
shallow waters from higher ground.
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