Ch. xxvn.] 



LINGULA FLAGS. 



577 



Lower Silurian forms, belong to the genera, Ogygia, Asapkus, and 

 Ckeirurus ; whereas those belonging to primordial types, or Bar 

 rande's first fauna, as well as to the Lingula flags of Wales, comprise 

 Conocoryphe* Olenus, several species, and Angelina. In the Upper 

 Tremadoc slates are found Bellerophon, Orthoceras, and Cyrtoceras, 

 all specifically distinct from Lower Silurian fossils of the same genera: 

 the Pteropod Theca ranges throughout these slates; there are no 

 Graptolites. The only Tremadoc species which, according to Salter, 

 is not peculiar, is Lingula Davisii, which ranges from the top to the 

 bottom of the formation, and links it with the zone next to be de- 

 scribed. The Tremadoc slates .are very local, and seem to be con- 

 fined to a small part of North Wales ; and Prof. Ramsay supposes 

 them to lie unconformably on the Lingula flags, and that a long inter- 

 val of time elapsed between these formations. 



Lingula Flags. — Next below the Tremadoc slates in North Wales, 

 lie micaceous flagstones and slates, in which, in 1846, Mr. E. Davis 

 discovered the Lingula named after him, and from which was de- 

 rived the name of Lingula Flags. f In these flags and shales, other 

 fossils were found by subsequent researches, which were observed to 

 differ specifically from those of the Llandeilo beds, or the lowest por- 

 tion of the Lower Silurian then palaeontologically known. Trilobites 

 of the genera Olenus and Conocoryphe (for genus, see fig. 667), and 

 other forms, which will soon be published by our Government Sur- 

 vey, were detected ; and Paradoxid.es (for genus, see fig. 666), another 



Fossils of the "Lingula Flags" or lowest Fossiliferous Rocks of Britain. 

 Fig. 661. Fig. 662. Fig. 663. 



Hymenocaris xermicauda, 



Salter. 



A Phyllopod Crustacean. 



i nat. size. 



" Lingula Flags " of Dolgelly, and Ffestinio 



Lingula Davisii, M'Coy. 



a. i nat. size. 



b. Distorted by cleavage. 



Olenus micrurus, 



Salter. 



i nat. size. 



X. Wales.i 



of Barrande's primordial forms of Bohemia, was also found both in 

 North and South Wales, in the black slates of this era. With these 



* This genus has been substituted for Barrande's Conocephalits, as the latter 

 term had been preoccupied by the entomologists. 



f This shell has since been referred by Salter to a subgenus Lingulella, but I 

 retain the original name in this chapter, because it has long been used by geolo- 

 gists in their designation of the beds where it is so abundant. 



% These figures were given in Sir R. Murchison's Siluria (2d ed., 1854), chap, ii 

 37 



