ferent coral polypes have contributed their quota
to the vast thickness of the carboniferous and Devonian strata. Then
as regards the latter group of rocks in America, the high authority
already quoted tells us:--

"The Upper Helderberg period is eminently the coral reef
period of the palaeozoic ages. Many of the rocks abound in
coral, and are as truly coral reefs as the modern reefs of the
Pacific. The corals are sometimes standing on the rocks in the
position they had when growing: others are lying in fragments,
as they were broken and heaped by the waves; and others were
reduced to a compact limestone by the finer trituration before
consolidation into rock. This compact variety is the most
common kind among the coral reef rocks of the present seas;
and it often contains but few distinct fossils, although
formed in water that abounded in life. At the fall of the
Ohio, near Louisville, there is a magnificent display of
the old reef. Hemispherical _Favosites_, five or six feet
in diameter, lie there nearly as perfect as when they were
covered by their flower-like polypes; and besides these,
there are various branching corals, and a profusion of
_Cyathophiyllia_, or cup-corals."[1]

[Footnote 1: Dana, "Manual of Geology," p. 272.]

Thus, in all the great periods of the earth's history of which we
know anything, a part of the then living matter has had the form of
polypes, competent to separate from the water of the sea the carbonate
of lime necessary for their own skeletons. Grain by grain, and
particle by particle, they have built up vast masses of rock, the
thickness of which is measured by hundreds of feet, and their area by
thousands of square miles. The slow oscillations of the crust of the
earth, producing great changes in the distribution of land and water,
have often obliged the living matter of the coral-builders to shift
the locality of its operations; and, by variation and adaptation to
these modifications of condition, its forms have as often changed. The
work it has done in the past is, for the most part, swept away, but
fragments remain; and, if there were no other evidence, suffice to
prove the general constancy of the operations of Nature in this world,
through periods of almost inconceivable duration.

VII.

ON THE METHODS AND RESULTS OF ETHNOLOGY.

Ethonology is the science which determines the distinctive characters
of