PART II. CHAPTER XXII. 



265 



Upper Silurian Rocks. 



England and Wales which was included in the ancient British 

 kingdom of the Silures. He has also formed four subdivisions 

 of the Silurian system, which he has designated as the Ludlow, 

 Wenlock, Caradoc, and Llandeilo, indicating thereby the places 

 where the prevailing characters of each formation are most per- 

 fectly exhibited. The following Table explains the succession 

 of these deposits.* 



UPPER SILURIAN ROCKS. 



Prevailing Lithological Thick- 

 Characters, ness. 



2000 ft. < 



2. Wenlock 

 formation. 





formation. 



Mollusca marine, of al- 

 most every order, the 

 Brachiopoda most 

 abundant. Serpula, 

 Corals, Sauroid fish, 

 Fuci. 



Wenlock ) Concretionary 

 limestone. ( limestone. 



Wenlock 

 shale. 



1 Argillaceous 

 I shale. 



f Marine mollusca of va- 

 rious orders as before. 



}-1800ft.^ Crustaceans of the 

 Trilobite family. 



j LNo vertebrata or plants. 



LOWER SILURIAN ROCKS. 



Flags of shelly' 

 limestone and 



bedded white 

 ^ freestone. 



) Dark coloured 

 $ calcareous flags. 



I Crinoidea, Corals, Mol- 



2500 ft. { lusca, chiefly Brachio- 

 poda, Trilobites. 



1200ft. $ Mollusca, Trilobites. 



UPPER SILURIAN ROCKS. 



Ludlow formation. This member of the upper Silurian 

 group, as will be seen by the above table, is of great thickness, 

 and subdivided into three parts. Each of these may be distin- 

 guished near the town of Ludlow, and at other places in Shrop- 

 shire and Herefordshire, by peculiar organic remains. The 

 most remarkable fossils are scales, ichthyodorulites, jaws, teeth, 

 and coprolites of fish, of the upper Ludlow rock.f As they 

 are the oldest remains of vertebrated animals yet known to geo- 

 logists, it is worthy of notice that they belong to fish of a high 

 or very perfect organization. 



See Murchison's Silurian System. 

 x 



t Ibid. p. 198, 199. 



