6 
SILUEIA. 
[Chap. I. 
cumstances, the Caradoc sandstones and Llandeilo flags in that of ' Lower 
Silurian Rocks/ 
" Simple as this classification may now appear, those versed in prac- 
tical geology can well understand what must have been the amount of 
examination employed in its perfect establishment. To comprehend the 
extent of the break in the history of the older strata which has been 
filled up by the study and classification of these rocks, the student has 
only to refer to the tabular view I have prepared, and compare it with 
other tables framed upon an antecedent state of geological knowledge. 
He will then perceive, that what is here presented to him as a well- 
ordered succession of great thickness (each subdivision of rocks being 
characterized by a corresponding suite of organic remains*), was formerly 
considered one assemblage, without definite sequence, and included under 
the unmeaning names of ' greywacke' or 'transition limestone.' I have 
already explained that the latter term has been as liberally bestowed 
(chiefly, however, by foreigners) upon the Carboniferous limestone, from 
which the Silurian rocks are separated by that enormous accumulation, 
the Old Red Sandstone ; whilst the organic remains of both these systems 
are entirely dissimilar from those of the carboniferous era Let 
us now proceed to consider these Silurian deposits in the natural order 
in which they appear in the south-west of Salop and adjacent parts of 
Herefordshire." 
During my early researches (1833), it was shown that the lowest of 
these fossil-bearing strata then known to me, including the Llandeilo 
flags, and their natural base the Stiper Stones, reposed, in the west of 
Shropshire, on a very thick accumulation of still older sediment, constitu- 
ting the Longmynd Mountain; and the strata of the latter, not then 
offering a vestige of former life, were at first termed * unfossiliferous 
greywacke 'f. 
As in examining all the strata of England and "Wales from south-east 
to north-west it had been found that there was a regular succession 
from younger to older rocks, so at the time when I propounded the 
Silurian classification (1835) it was the belief of all geologists who had 
examined the country J, that the slaty rocks of North "Wales rose up from 
beneath my Silurian types of Shropshire and the counties of Montgomery, 
Hereford, and Radnor. In this belief I coincided, without surveying 
the north-western tracts of Wales. Hence another term, or that of 
* These organic remains were laid before the have designated as ' Cambrian ' only those rocks 
Geological Society, and named, in each succeeding of Wales which, like my original type the Long- 
Session from 1831 to 1838, when the large work, mynd, underlie all the strata with Silurian fossils, 
the ' Silurian System,' was completed and pub- I See all the early geological maps, and even 
lished. the last edition of the Map of G-reenough (1839). 
t The Stiper Stones were classed by me in 1833 In 1838 also, Professor John Phillips still held 
and 1834 as the base of the' overlying series, which this belief, as well as myself and others, and gave 
was termed Silurian as early' as 1835. See Phil, in the Penny Cyclopaedia (art. Geology) a sec- 
Mag, vol. vii. p. 46, with a diagram showing such tion across Britain, in which the Snowdon and 
Silurian rocks reposing on ' unfossiliferous grey- North-Welsh rocks are placed below the Caradoc 
wacke.' The Government Geological Surveyors and Llandeilo formations. 
