y of the
earth's past. The only conspicuous attempt to classify the strata was
that made by Werner, who divided the rocks into three systems, based on
their supposed order of deposition, and called primary, transition, and
secondary.

Though Werner's observations were confined to the small province of
Saxony, he did not hesitate to affirm that all over the world the
succession of strata would be found the same as there, the concentric
layers, according to this conception, being arranged about the earth
with the regularity of layers on an onion. But in this Werner was
as mistaken as in his theoretical explanation of the origin of the
"primary" rocks. It required but little observation to show that the
exact succession of strata is never precisely the same in any widely
separated regions. Nevertheless, there was a germ of truth in Werner's
system. It contained the idea, however faultily interpreted, of a
chronological succession of strata; and it furnished a working outline
for the observers who were to make out the true story of geological
development. But the correct interpretation of the observed facts could
only be made after the Huttonian view as to the origin of strata had
gained complete acceptance.

When William Smith, having found the true key to this story, attempted
to apply it, the territory with which he had to deal chanced to be one
where the surface rocks are of that later series which Werner termed
secondary. He made numerous subdivisions within this system, based
mainly on the fossils. Meantime it was found that, judged by the
fossils, the strata that Brongniart and Cuvier studied near Paris were
of a still more recent period (presumed at first to be due to the latest
deluge), which came to be spoken of as tertiary. It was in these beds,
some of which seemed to have been formed in fresh-water lakes, that many
of the strange mammals which Cuvier first described were found.

But the "transition" rocks, underlying the "secondary" system that Smith
studied, were still practically unexplored when, along in the thirties,
they were taken in hand by Roderick Impey Murchison, the reformed
fox-hunter and ex-captain, who had turned geologist to such notable
advantage, and Adam Sedgwick, the brilliant Woodwardian professor at
Cambridge.

Working together, these two friends classified the

transition rocks into chronological groups, since familiar to every one
in the larger outlines as the Silurian system (age o