76 STRATIGRAPHICAL GEOLOGY 



Brachiopoda. Lingulella Davisii, Orthis lenticiilaris (and in 



Tremadoc). 

 Gastropoda. Bellerophon cambrensis. 



Upper Cambrian (Tremadoc) 



Hydrozoa. Dictyograptus socialis ( = Dictyonema), Bryograptus 



Callavei, B. Kjerulfi. 



Echinoderma. Dendrocrinus cambrensis, Palseasterina ramseyensis. 



Trilobita. Asaphellus Homtrayi, Ogygia scutatrix, Niobe Honi- 



frayi, Angelina Sedgwicki, Sphrerophthalmus alatus, 

 Peltura punctata. 



Brachiopoda. Lingulella lepis, Obolella Belti. 0. sabrinse, Orthis 



lenticularis, and 0. Carausi, Orthisina festinata. 



Lamellibranchia. Palsearca Hopkinsoni, Glyptarca primseva, Ctenodonta 

 menapiensis. 



Gastropoda. Hyolithes cuspidatus, Conularia Homfrayi, Bellero- 



phon arfonensis. 



Cephalopoda. Orthoceras sericeum, 0. mendax, Cyrtoceras praecox. 



C. BRITISH CAMBRIAN ROCKS 



Range and. Relation to Rocks below. Cambrian rocks 

 rise to the surface in several parts of England and Wales, as well 

 as in Ireland and Scotland, but they nowhere occupy any large 

 tract of country and they exhibit several very different facies, so 

 that it is with some difficulty that the component members of 

 these isolated exposures can be compared with one another. 



In Wales, the typical area, there are four districts where 

 Cambrian strata emerge from beneath the overlying Ordovician, 

 namely in Pembrokeshire, Merionethshire, Carnarvonshire, and 

 Anglesey. In England there are six outcrops, but all are small ; 

 these are (1) The Malvern Hills, (2) The Wrekin area in Shropshire, 

 (3) The Lickey (N. Worcestershire), (4) near Nuneaton in Warwick- 

 shire, (5) The Lake District, and (6) The Isle of Man. 



In Ireland rocks which are believed to be of Upper Cambrian 

 age occur in Wicklow and Wexford, but they contain very few 

 organic remains, and none of the Welsh Cambrian fossils have yet 

 been found in them. 



In Scotland they have only yet been recognised in the extreme 

 north-west (Sutherland, Ross, and Skye), where they consist mainly 

 of limestones, and thus exhibit a very different facies from those 

 occurring in the more southern areas. 



Wherever the base of the Lower Cambrian Series is exposed, it 

 is seen to rest unconformably upon an eroded and planed down 

 surface of the Archaean rocks. This is conspicuously the case in 

 Scotland and in most of the English localities, but the base is not 

 exposed in Cumberland, the Isle of Man, nor in Ireland. 



