lvi INTRODUCTION. 
not above, but below, the Upper Cambrian rocks of the neighbourhood. It is not a Silurian 
group, to be packed (as is done in all the typical Silurian sections) near the base of the 
Wenlock shale—to which it has no relations except those of an accidental and discordant 
contiguity. A greater and more injurious mistake, in the collocation of contiguous groups, 
has not been committed during the progress of British Paleozoic Geology. The fact is, 
that the author missed the true relations of the May Hill sandstone to his upper groups; 
and, consequently, missed both the physical and paleontological base of his own “System.” 
When he passed below the May Hill sandstone, he overstepped the true and connected 
sequence of the Silurian deposits; and he descended at once, and without being conscious 
of it, among the vast and complicated groups of Cambria, through which he had never 
made his way, and with which he was then very imperfectly acquainted: and, however 
laboriously and well he did the work of the naturalist and collector, he inevitably failed, so 
far as regarded his two lower groups, in the real task-work of the geologist. He neither 
truly interpreted the Caradoc group; nor did he define (even with approximate truth) the 
place of the Llandeilo group in the great Cambrian Series. Without a good definition of 
such groups, their nomenclature, as parts of a system, is untenable, and absolutely without 
meaning. 
But if the author of the “Silurian System” overstepped its base, mistook the relations 
of his lower groups, and was led, thereby, to a nomenclature which was untrue to nature ; 
he has since then done far greater injury to the cause of physical truth and scientific pro- 
gress, by a desertion of the principles he once vindicated, and on the happy application of 
which rests the best part of his scientific fame. For what is the system of classification 
and nomenclature that he has for some years been endeavouring to enforce? <A classifi- 
cation and nomenclature on the well-combined evidence both of sections and fossils, whereby 
group is linked to group ina natural order? No! But a classification derived from fossils 
only, and of almost boundless application. The “Lower Silurian” groups, in the very sections 
which were assumed as typical, were misinterpreted in the “Silurian System,” and were out 
of their true place in the general sections of North and South Wales. Yet while this is 
virtually admitted, all the rocks of the Principality which contain the fossils of these mistaken 
lower Silurian groups, and also rocks which descend many thousand feet below them, are 
now to be called Silurian: and the Llandeilo formation is to pass as the name for all the 
vast groups which are here described, as the Cambrian series, in the Tabular View! 
After the history of the Llandeilo Flag, I should have thought it far better taste to 
have suppressed the name Llandeilo from any prominent place in Paleozoic classification 
and nomenclature. But without discussing a point of taste, this I dare to affirm, that the 
title-page and the map, of the new work called “ Si/wra,” are in themselves as severe a 
satire as the pen could write against the work, if it is to be considered as a scheme which 
is to settle the grouping and geographical nomenclature of the older Paleozoic rocks of 
England. The Llandeilo flag was the lowest group of the “Silurian System ;” but all old 
rocks below the upper Ludlow must be Silurian; therefore the oldest rocks of Wales are 
Llandeilo flag! I know no better logic whereby the author of the System can maintain his 
