ed Marl inclusive; or,
in other words, to the great Secondary division. The Coal Measures had,
however, been previously better known, from their economic importance,
and the number of the workings opened among them, than the deposits of
any other system; and ere the publication of the map of Smith, Cuvier
and Brogniart had rendered famous all over the world the older Tertiary
formations of the age of the London Clay. But both ends of the
geological scale, comprising those ancient systems older than the Coal,
and representative of periods in which, so far as is yet known, life,
animal and vegetable, first began upon our planet, and those systems of
comparatively modern date, representative of the periods which
immediately preceded the human epoch, were equally unknown. The light
fell strongly on only that middle portion of the series on which the
labors of Smith had been mainly concentrated. The vast geologic bridge,
which, like that in the exquisite allegory of Addison, strode across a
"part of the great tide of eternity," "had a black cloud hanging at each
end of it." And such was the state of geologic science when, in 1814,
Dr. Chalmers framed his scheme of reconciliation.

Since that time, however, a light not less strong than the one thrown by
William Smith on the formations of the Lias and the Oolite has been cast
on both the older and the newer fossiliferous systems. Two great gaps
still remain to be filled up,--that which separates the Palaeozoic from
the Secondary division, and that which separates the Secondary from the
Tertiary one. But they occur at neither end of the geological scale.
Mainly through the labors of two distinguished geologists, who, finding
the geologic school of their own country distracted by a fierce and
fruitless controversy, attached themselves to the geologic school of
England, and have since received the honor of knighthood in
acknowledgment of their labors, both ends of the geologic scale have
been completed. Sir Roderick Murchison addressed himself to the
formations older than the Coal, more especially to the Upper and Lower
Silurian systems, from the Ludlow rooks to the Llandeilo flags. The Old
Red Sandstone too, a system which lies more immediately beneath the
Coal, has also been explored, and its various deposits, with their
peculiar organic remains, enumerated and described. And Sir Charles
Lyell, setting himself to the other extremity of the scale, has wrought
out the Tertiary fo