xeVi POSTSCRIPT TO THE INTRODUCTION. 
is not the fact: for the real break, and the only great break, in the older Paleozoic 
series is at the base of the May Hill Sandstone. 
Professor Phillips seems still inclined to retain the name Upper Caradoc—first proposed 
by himself—and to regard it as a “Transition group” between his Upper and Lower Silurian 
rocks (Manual, p. 103). He was the first to point out a distinction between the (so-called) 
Upper and Lower Caradoc; but he did not follow it into all its consequences; nor do I 
think that the sections of the Malverns and the neighbouring country gave him the 
ready means of doing so in 1842, while he was working with the clog of an erroneous 
“Lower Silurian” nomenclature. Be this as it may, the full and true distinction was 
first pointed out by Professor M*Coy and myself; and though it was at first opposed 
by the gentlemen of the Government Survey, it was, not long afterwards, adopted by 
them. 
So long as the collective Caradoc group was placed at the top of, and was classed 
with the (so-called) “Lower Silurian” rocks, no one could object to such a name as Upper 
Caradoc. But after it had been separated into two distinct physical and paleontological 
groups (as isnow done in the Manual, p. 105), the name “Upper Caradoc” ceased to be an 
appropriate term. I am certain that this was the opinion of the late Professor Forbes*: 
and I did not propose a new name for the higher group, as Professor Phillips supposes (Manual, 
p. 115, note): but, to make the least possible innovation, I replaced an old name, May Hill 
Sandstone (first adopted by the author of the Silurian System), as the appropriate designation 
of that arenaceous group which is the physical base of the true Silurian rocks. 
Before I leave this comment on what some may think a minute question—one, how- 
ever, of no small importance—I would suggest the expediency of repudiating altogether the 
name “Caradoc” as the designation of the great and very ill-defined groups of strata at the 
top of the Cambrian series of South Wales; and of using in its place the name “ Horderley 
sandstone”—as a better general term to define, approximately, any of the shelly sandstones 
and conglomerates which appear near the top of the Upper Bala group—as a term also 
which involves us in no ambiguity arising out of previous mistakes in the definition of 
the (so-called) Upper and Lower Caradoc sandstone. 
In following out the previous remarks, I request the reader to turn back to 
pp. xl and xli of the Introduction; and afterwards by help of the great map of the 
Government Survey, or of the reduced map prefixed to “Siluria”—to test the truth of 
what I have stated, as to the Cambrian strike, and the peculiar place and office of the 
May Hill Sandstone, which is the true Silurian base. There have been enormous dislocations 
in North America (below the Potsdam sandstone), of which we have, perhaps, no trace 
in England; but of which there may be a trace in Ireland; and we need not doubt that 
* I have alluded to the opinion of Professor Forbes on this question of nomenclature (supra, p. lii); and he had 
previously expressed himself much more distinctly on this point in the last conversation he held with Professor M°Coy 
and myself, some time before the meeting of the British Association in 1854. 
