the Cambrian contained no fossils that differed from those of the Lower
Silurian. Whereupon Sedgwick undertook a re-examination of the Welsh
rocks with the assistance of J.W. Salter, the palaeontologist; and in
1852 he included the Llandeilo and Bala beds (Silurian) in the Upper
Cambrian. Two years later Murchison brought out his _Siluria_, in which
he treated the Cambrian system as a mere local facies of the Silurian
system, and he included in the latter, under J. Barrande's term
"Primordial zone," all the lower rocks, although they had a distinctive
fauna.

Meanwhile in Europe and America fossils were being collected from
similar rocks which were classed as Silurian, and the use of "Cambrian"
was almost discarded, because, following Murchison, it was taken to
apply only to a group of rocks without a characteristic fauna and
therefore impossible to recognize. Most of the Cambrian rocks were
coloured as Silurian on the British official geological maps.

Nevertheless, from 1851 to 1855, Sedgwick, in his writings on the
British palaeozoic deposits, insisted on the independence of the
Cambrian system, and though Murchison had pushed his Silurian system
downward in the series of rocks, Sedgwick adhered to the original
grouping of his Cambrian system, and even proposed to limit the Silurian
to the Ludlow and Wenlock beds with the May Hill Sandstone at the base.
This attitude he maintained until the year of his death (1873), when
there appeared his introduction to Salter's _Catalogue of Cambrian and
Silurian Fossils._

It is not to be supposed that one of these great geologists was
necessarily in the wrong; each had right on his side. It was left for
the subsequent labours of Salter and H. Hicks to prove that the rocks
below the undoubted lower Silurian of Murchison did indeed possess a
characteristic fauna, and their work was confirmed by researches going
on in other countries. To-day the recognition of the earliest
fossil-bearing recks, below the Llandeilo formation of Murchison, as
belonging to the Cambrian system, and the threefold subdivision of the
system according to palaeontological evidence, may be regarded as firmly
established.

It should be noted that A. de Lapparent classifies the Cambrian as the
lowest stage in the Silurian, the middle and upper stages being
Ordovician and Gothlandian. E. Renevier proposed to use _Silurique_ to
cover the same period with the Cambrian as the lowest series, but these
differen