^tORlllS— E RITIsH FO.SsILS. 



233 



especially those which would be suited to live in a sandy bottom. 

 Ammonites and Belemnltes are in unusual numbers, and many of them 

 of great size. It is also distinguished by some very large Pectons, and a 

 fine Gryphica {G. gigantea), a species of Pinna, and by univalves equally 

 gigantic. ]\Iost of the fossils exist in the form of casts : and the ancient 

 genera, Spirifer, Leptoena, Orbicula, and Ijingula, so abundant in the 

 older formations, still linger here. Eemains of Pentacrinites, one of the 

 most curious and beautiful of the Crinoidea, vertebrce of Ichthyosauri, 

 with the solitary humerus of a Pterodactyle, have also been noticed. 

 The stone is hard, and the fossils difficult to extract in consequence ; 

 yet, from their abundance and variety, the collector is sure to secure 

 a characteristic and instructive series. The most prolific localities 

 in Gloucestershire are the quarries at Bredon, Alderton, Dumbleton, 

 Gretton, Churchdown, and Hewlett's Hill, close to Cheltenham. 



{To he continued.) 



BRITISH FOSSILS, STPATIGRAPHICALLY A11PvA:NT{ED. 

 Bi' John jMoeris, F.G.S. 

 I. PALEOZOIC S Y S T E jS[ . 



(Continn-id jrora page 194.) 

 G. LLANDOVERY ROCKS, OR JIIDDLE SILl'RLVN. 

 Wales, Siiropshiiit:. 

 &c. 



Cumberland. 



Scotland. 



Ireland. 



Upper Llandovery I 

 May Hill Sandstoiiel 

 Lower Llandovery j 

 Plynlymon rocks, i 



Hard siliceous 

 sandstones or Con- 

 iston grits. 



Shelly sandstones 

 and shales of Saugh 

 Hill, and MuUoch 

 Hill, Ayrshire. 



Conglomerates, 

 sandstones, and 

 schists, near Maam, 

 &c. Cirahyay, Ua'gool, 

 Mayo. 



The Llandovery rocks were so named by Sir 11. Murchison from the 

 locality in South Wales where they are most fully developed, and 

 where their physical relations to the formations above and below them 

 are clearly exposed. These rocks constitute an intermediate place in 

 the Silurian table, connecting, by some of their contained organic 

 remains, the fauna of the upper and lower Silurian groups. The 

 upper Llandover}' rock contains many shells common to the Wcnlock 

 beds, and is considered to form the natural base of those deposits ; on 

 the other hand, the lower Llandovery is related by its fossils to the 

 Caradoc beds below, and both members of this formation are united hy 

 haying certain fossils in common and peculiar to them, but are chiefly 

 characterized by the abundance of some species of Petraia, Atrypa, 



u 



