Chap. V.] LOCAL BKEAKS IN SUCCESSION. 101 
At the Malvern Hills the lowest zone, or the equivalent of the Lingula-flags, 
is succeeded at once by the Upper Llandovery rocks, — the true Llandeilo and 
the Caradoc beds being also excluded, as at May Hill. In Shropshire, or 
my typical tract, no such hiatus occurs ; for there the original Caradoc 
formation exhibits a copious series of shelly sandstones (from 4000 to 
5000 feet thick) rising from beneath the Upper Llandovery rock. 
The reader must here, however, be reminded that in the original Silu- 
rian region there are large rocky districts of Shropshire and Eadnorshire, 
like those of Shelve and Builth, in which the Llandeilo Flags are not fol- 
lowed by the Caradoc rocks. The latter formation, of such large dimen- 
sions elsewhere, has there been entirely omitted, and the older deposit of 
Llandeilo is at once covered by a thin band only of the Upper Llandovery 
sandstone, followed by the Upper Silurian shales. In those cases, it is 
manifest that powerful, but limited and local, oscillations of the sea- 
bottom have taken place, by which the black muddy sediment, with its 
Trilobites and Shells, was raised up to constitute the Llandeilo Flags, and 
was placed beyond the influence of the waters under which the true 
Caradoc sandstones were accumulated in many other districts. Yet the 
older Llandeilo rocks, so elevated, were again depressed beneath the sea, to 
receive on their upturned edges the accumulations of the Pentamerus 
band and the overlying Upper Silurian series (see sections, p. 59). 
The geologist who reasoned from such phenomena only, might be led 
to believe that a general break had occurred in the heart of the Lower 
Silurian rocks, or between the Llandeilo and Caradoc formations ; but in 
this he would greatly err, for no such hiatus exists over a large region of 
"Wales. On the contrary, by extending our observations, we find that the 
absence of the great Caradoc deposit in two or three tracts is, after all, 
a local phenomenon, inasmuch as we recognize the spread of that forma- 
tion over a wide region of the Principality, where it lies symmetrically 
upon the Llandeilo rocks. 
When the Upper Silurian rocks shall have been described, two synoptic 
tables will be placed before the reader, — one showing the omissions of certain 
strata in some tracts and their full sequence in others, the other being a 
generalized table of the whole. In the meantime let us remember that, 
whatever may have been the amount of disturbance of the ancient sea- 
bottom at the conclusion of the true Caradoc deposit, there are districts both 
in North and South "Wales where no signs of such movements can be de- 
tected, but where all the sediments, from the Llandeilo, through the Cara- 
doc, to the Lower Llandovery rocks inclusive, seem to have succeeded each 
other quietly, or at all events without exhibiting any rupture in their 
succession. Above all, it is to be recollected that, whatever may have 
been the amount of physical disturbance between the lower and the upper 
member of the Llandovery rocks, the organic remains of that formation 
unquestionably connect it with the Lower as well as the Upper Silurian 
