Chap. V.] INTERMEDIATE CHARACTER OF LLANDOVERY ROCKS. 
85 
CHAPTEB V. 
LLANDOVERY ROCKS (TRANSITION FROM LOWER TO UPPER 
SILURIAN). 
TUIS FORMATION SHOWN TO BE OF INTERMEDIATE CHARACTER, CONTAINING BOTH LOWER 
AND UPPER SILURIAN FOSSILS, WITH SOME PECULIAR TYPES. ASCENDING ORDER OF THE 
WHOLE GROUP NEAR LLANDOVERY IN SOUTH WALES, WHERE MOST DEVELOPED. THE 
UPPER PORTION ALONE EXHIBITED IN RADNORSHIRE, SHROPSHIRE, HEREFORDSHIRE, THE 
MALVERN HILLS, MAY HILL, TORTWORTH, THE LICKEY HILLS, ETC. TARANNON SHALES, 
OR BASE OF THE UPPER SILURIAN IN NORTH WALES. 
In my earlier publications, the whole group of strata to which attention 
is now invited was placed at the summit of the Lower Silurian rocks. The 
progressive researches and labours of my cotemporaries, however, have 
for some time led me to admit that, whilst the lower and larger portion 
of this formation is related, through numerous organic remains, to the in- 
ferior half of the system, the higher member, though also containing some 
of the lower types, is, by many of its fossils, more naturally connected 
with the Upper Silurian *. At the same time, the formation is eminently 
characterized throughout by certain Pentameri peculiar to it, which are 
not known either in the subjacent or superjacent deposits, and also by 
some species of other shells which never rise into the Wenlock (or true 
Upper Silurian) rocks. A short chapter is therefore devoted to the con- 
sideration of this group, showing its intermediate character and varied 
development in different localities. 
Though not recognizable in the northern or central parts of the Silurian 
region, the inferior member of the formation is fully exposed in extensive 
tracts of South Wales to the north and west of Llandeilo, particularly near 
Llandovery, where it was formerly described in detail (Sil. Syst. p. 351). 
Let us first, then, consider the nature and contents of these rocks as seen in 
ascending order in the last-mentioned tract, where both their members are 
exposed, and afterwards treat of them in certain districts where the lower 
member of the group is wanting and the uppermost subdivision alone is 
visible. 
In the first edition of this work, all these rocks were termed ' Upper 
Caradoc ; ' but that term was set aside in the last edition. The local name 
of ' Llandovery Eocks ' was then taken, from the district where clear phy- 
sical relations are seen of the transition from the Caradoc formation beneath, 
* This last feature was first pointed out by memoir on the May Hill Sandstone (Phil. Mag. 
Professor Sedgwick and Professor M'Coy in their ser. 4. vol. viii. 1854, p. 301). 
