336 
THE fiEOLOGIST, 
HETrROPODA. 
r.ollerophon trilol):!tns, Son'. Sil. 'i.vO. 
expiinsus. <S'o?(', S. S. 01.). 
Bellproplion bilobatns, Soir. S. S. G4;j. 
dilatatus, Smi: S. S. 1)27. 
subdccussatus, M'Coy, P. F. .-Ul. 
Pteropoda. 
Conularia Sowcrbyi, Defr.^W. 234. Cyrtolites Scoticus, M'Cay, P. F. 301. 
quadrisulcatus, Sil. syst. Pterothcca transversa, iSaiter, Sil. 218. 
Cephalopoda. 
Lituites cornu-arietes, Sow. S. S. 643. Orthoocras couiciini, S'ifl. S. S. G42. 
coralliforrae, 31' Co;/, S. F. p. 8. 
tenuicinctum, J'orll. G. R. 371. 
tenui.striatum, Miinsf. 
ibex, Sou: S. 8. 613. 
Phragmocera.s comprcssum, Soir. Sil. 
235. 
Tretoceras bisiplionatura, Sow. Sil. 235. 
undosus, Sow. sp. S. S 642. 
Cyrtoceras approximatum. Sow. S. S. 
642. 
Orthoceras Barrandei, Salt. G. J. 7. t. 0. 
angulatum, Wuhl. Sil. 234. 
approximatum. 
bilineatum. Hall, V. N. Y. t. 43 
IbuUatum, Soxv. Sil. 234. 
D. UPPEIl SILURIAN, (MuEcmsoN.) 
Silurian, Sedgwick; Murchisonian, D'Orbigny; UppEa Sit.urian, rhilUps, 
Lijell, Jukes, &c. 
Wales, SnROPsniRE. Cumderland, &o. Scotland. Ireland. 
Tilestones. Downton 
sandstone. 
Tilestone?. 
Slates. 
Upper Lud- 
low, Aymes- 
try limestone, 
Lower Ludlow, 
Wenlock limeet., | 
Wenlock shale, I 
Woolhope limest. | 
Denbigh grits, | 
Tarannon shale. J 
f Coarse grits, 
flags, slates, lime- 
stone, (Kendal 
- group, Sedg- 
I wick.) 
I Windermere 
[rocks, (Sharpe.) 
' Irelcth slates, 
limestones, grits, 
coarse slates, 
(Ireletli group, 
Sedgwick.) 
f Lesmahago 
schists, dark- 
coloured schists | 
and clay slates, 
\ with calcareous j- 
nodules, Lanark- I 
1 shire. Schistose | 
I strata of the | 
I Pcntland Hills. J 
f Grey flags and 
slates, 1,000 ft. 
) Grey flags and 
I slates, purple 
J .slates and grits, 
I with beds of 
j felspathic ash, 
I 2,o00 ft. Dingle, 
I Clogher, &c., 
[ Ughool, Mayo. 
In the typical district of Siluria — the border counties of England 
and ^Yales, the Upper Silurian group consists of argillaceous, arena- 
ceous, and calcareous strata, or shales, mudstones, sandstones, conglo- 
merates, argillaceous and concretionary limestones, indicating different 
conditions of accumulation, and probably varying from littoral to 
deep-sea deposits, the limestones showing periods of repose, of coral 
growth, and a greater abundance of organic life than the shaly and 
arenaceous sediments. This group is subdivisible into an upper and 
lower series — the Ludlow and Wenlock rocks, with the thickness of 
about G, 000 feet. In other districts, the thickness varies, and the cal- 
careous bands are less abundant ; tlius the "Woolhope, Wenlock, and 
Aymestry limestones are but indistinctly exhibited towards the west of 
the typical country. In Scotland and Ireland, also, these strata present 
a more arenaceous, and sometimes conglomeratic, character. 
'J'lio upper Llandovery rocks or May nil! sandstone of Piofpssor 
