236 



THE GEOLOGIST. 



ITetf.eopoda 

 C43. 



Belleroplion trilob.itu?, Soir. Sil. 

 cxpausus. Soir, s. s. ulo. 



Eellcrophon l3ilobatus, Sou: 

 dilatJitus, Sow. S. 8. Gi^T. 

 subdecussatus, JIT Co?/, P. F. 311. 



PTEEOrODA. 



Conularia Sowcrbyi, Dcfr. Sil. 234. Cyrtolites Scoticus, M'Coi/, P. F. 301 . 



quadi'isulcatus/Sil. svst. Pterotheca transversa, Salter, Sil. 218, 



Cephaxopoda. 



Lituites cornu-ariete?. S. S. G43. 



undosus. Sou-. $}■>. S. s 042. 

 Cyrtoceras approximatum, Sou: S, S. 



642. 



Orthoceras Barraiidei. Salt. G. J. 7. t. 9, 

 augulatum, ir. /f'. Sil. 234. 

 approximatuin. 



biHneatum, Hall, P. N. Y. t. 43 

 bullatum. Sou: 8il. 234. 



Orthoceras couicuni, Satl. S. S. 642. 

 coralliforme, JrCoj/, 8. F. p. 8. 

 tenuiciuctum, Fortl. G. R. 371. 

 teuuistriatuin, Jliai.^t. 

 ibex, Sou: 8. 8. 613. 

 Phragmoceras compressum, Son: Sil. 

 235. 



Tretoceras bisiishonatum, Sou: Sil. 235. 



siLrEiAX, Sedgwidc 



D. UPrER SILURIAN, (iluRCHisox.) 

 MrKciiisoxiAN, D'Orhigny; Upper Silurian, ritilUps, 



Lyell, Jukes, &c. 



Walls, Shropshire. Cujiberland, Scq. 



Tilestones. Downtou 

 sandstone. 



Tilestones. 



Upper Lud- ^ 

 low, A vines- j 

 try limestone, ] 

 Lower Ludlow, | 

 Wenlock limest., [- 

 Wenlock shale, | 

 Woolhope limest. | 

 Denbigh grits, | 

 Tarannon shale. J 



f Coarse grits, | 



flags, slates, lime - 

 I stone, (Kendal 

 -{ group. Sede:- 

 I wick.) 



I Windermere 

 [rocks, (Sharpe.) [ 

 fireleth slates, 

 } limestones, grits, 

 -{ coarse slates, 

 I (Ireleth group, 

 [Sedgwick.) 



Scotland. 



Lesmahago ~) 

 schists, dark- j 

 coloured schists | 

 and clay slates, j 



Ireland. 

 Slates. 



f Grey flags and 

 I slates, 1,000 ft. 

 j Grey flags and 

 j slates, purple 

 I slates and grits, 



Kith calcareous}- 4^.^^ ^^^^ 



j felspathic ash, 

 2,500 ft. Dingle, 



nodules, Lanark- 

 j shire. Schistose | 

 I strata of the ] 

 [Pentland Hills. J 



I Clogher, &c. 

 l_ Ughool, Mayo. 



In the t3-pical district of Siluria — the border counties of England 

 and Wales, 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 6,000 feet. In other districts, the thickness varies, and the cal- 

 careous bands are less abundant ; thus the Woolhope, Wenlock, and 

 Aymcstry limestones are but indistinctly exhibited to^-ards the west of 

 tlic typical country. In Scotland and Ireland, also, these strata present 

 a more arenaceous, and sometimes conglomeratic, character. 



Tlio upper Llandoverv rooks or Mav Hill sandstone of Professor 



