Belt — On the " Lingula Flags." 



495 



each. Lithologically, the Dolgelly Group is characterised by soft 

 black slates, with a black streak ; the Festiniog Group by hard 

 micaceous flags, and the Maentwrog Group by dark-blue, jointed, 

 ferruginous slates. 



Before passing on to a detailed account of these rocks and their 

 fossil contents, and in order to exhibit clearly their position in the 

 Cambrian system, I give below a table of the whole of the Cambrian 

 rocks, showing the proposed classification, and the range of the 

 genera. I have not included Calymene, Homalonotus, and Nucida, 

 recorded by Messrs. Salter and Hicks from rocks at St. David's — 

 believed by them to be of Tremadoc age ^ — as no Tremadoc species 

 have been found, and all the trilobites belong to Silurian genera. 

 They will probably form a Lower Arenig Group. 



Table of the Cambrian Eocks showing the Eange of the Genera. 



Genera. 



Lower Cambrian. 



Upper Cambrian. 



Bangor 



Slates. 



Harlech 

 Grits. 



Menevian 

 Group. 



Maentwrog 

 Group. 



Festiniog 

 Group. 



Dolgelly 

 Group. 



Tremadoc 

 Group. 



Paradoxides 



Anopolenus 



Microdiscus 



Erinnys 





- 













. .* 



* 



. # 



* 

 * 



* 



* 

 * 





— 



Holocephalina ... 

 Conocoryphe 





Olenus 







— 



Parabolina 





Peltura 



Sphseropthalmiis... 

 Dikelocephalus ... 

 Niobe 



Angelina 



Cheirurus 



Ampyx 



Asaphus 



Ogygia ,,. 



Hymenocaris 



Lingulocaris 



Leperditia 



Protocystites 



Bellerophon 





Obolella 



















* 



OrtMs 



— 











. * 



* 



« 



* 



Theca .. 



Cyrtotheca 













Conularia 



Orthoceras 



Dictyonema 



Protospongia 



Buthotrephis 





The Genera marked thus * pass upwards. 

 1 Report Brit. Assoc, 1866, p. 184. 



fTo he continued. J 



