f invertebrates) and
the Devonian system (age of fishes)--names derived respectively from the
country of the ancient Silures, in Wales and Devonshire, England. It
was subsequently discovered that these systems of strata, which crop out
from beneath newer rocks in restricted areas in Britain, are spread out
into broad, undisturbed sheets over thousands of miles in continental
Europe and in America. Later on Murchison studied them in Russia,
and described them, conjointly with Verneuil and Von Kerserling, in
a ponderous and classical work. In America they were studied by Hall,
Newberry, Whitney, Dana, Whitfield, and other pioneer geologists, who
all but anticipated their English contemporaries.

The rocks that are of still older formation than those studied by
Murchison and Sedgwick (corresponding in location to the "primary" rocks
of Werner's conception) are the surface feature of vast areas in Canada,
and were first prominently studied there by William I. Logan, of the
Canadian Government Survey, as early as 1846, and later on by Sir
William Dawson. These rocks--comprising the Laurentian system--were
formerly supposed to represent parts of the original crust of the earth,
formed on first cooling from a molten state; but they are now more
generally regarded as once-stratified deposits metamorphosed by the
action of heat.

Whether "primitive" or metamorphic, however, these Canadian rocks, and
analogous ones beneath the fossiliferous strata of other countries,
are the oldest portions of the earth's crust of which geology has any
present knowledge. Mountains of this formation, as the Adirondacks and
the Storm King range, overlooking the Hudson near West Point, are the
patriarchs of their kind, beside which Alleghanies and Sierra Nevadas
are recent upstarts, and Rockies, Alps, and Andes are mere parvenus of
yesterday.

The Laurentian rocks were at first spoken of as representing "Azoic"
time; but in 1846 Dawson found a formation deep in their midst which was
believed to b e the fossil relic of a very low form of life, and after
that it became customary to speak of the system as "Eozoic." Still more
recently the title of Dawson's supposed fossil to rank as such has been
questioned, and Dana's suggestion that the early rocks be termed merely
Archman has met with general favor. Murchison and Sedgwick's Silurian,
Devonian, and Carboniferous groups (the ages of invertebrates, of
fishes, and of coal plants, respectively) are to