452 SPECIAL GEOLOGY. 



The thickness of the English group is estimated on an 

 average -at 10,000 feet, but in Scotland it is conjectured to 

 be much greater. In addition to the localities given in the 

 above table, it is largely developed in the south of Devon, in 

 Shropshire, Herefordshire, and the border-counties of Wales ; 

 on the Continent it occurs in Germany, and extends over 

 vast areas in Eussia, south of St. Petersburg!!. 



IDENTITY or THE OLD BED SANDSTONE or HEREFORD AND 

 DEYON. Doubts were entertained for a considerable period 

 as to whether the old red sandstone of Devon and that of 

 Hereford were identical; these doubts being chiefly suggested 

 by the fact that the strata of Devon contained shells of the 

 genera OrtJiis, Spirifera, Productus, Terebratula, &c., which 

 were not found in the rocks of Hereford; whilst the 

 latter afforded fishes which were not found in those 

 of Devon. Sir B. Murchison, however, in his first visit 

 to Bussia, in 1840, discovered, in strata appertaining to the 

 old red sandstone, the fishes of Hereford and Scotland, in 

 the same beds with the shells of Devon. Sir B. Murchison 

 and Professor Sedgwick have further shown that the equiva- 

 lents of the Devon rocks exist in the Bhenish provinces, 

 and adjacent parts of G-ennany. Certain corals, as Cya- 

 thophyllum ccespitosum, Forties pyriformis, and Favosites 

 polymorpka, with the shells JMIegalodon cucullatus, Cal- 

 ceola sandalina, and StrygocepJialus Burtini are characteristic 

 of the rocks of Devon, and of the Eifel in Germany. 



Among the gasteropoda are species of Pleurotomaria, 

 Euomphalus, Bellerophon, Nerita, and Natica, &c.; the 

 cephalopoda are represented by the genera Aganides, 

 Cfymenia, Gyroceras, Gyrtoceras, Stenoceras. The articulata 

 of this group belong to the family of Trilobites. The rocks of 

 Devon have yielded specimens of Calymene, Asaplius, 

 Harpes, Homalonotus, and Brontes, one species of which 

 (_B. fldbellifer) is common to the Devonian rocks of the 

 Eifel and South Devon. 



This group is well developed in Germany : the limestones 

 of the Eifel, so long celebrated for their fossil remains, 

 belong to the lower part of this system, and lie in a basin 

 supported by Silurian rocks. 



In Bussia the Devonian system occupies a wide area 

 south of St. Petersburgh, and contains a fauna similar to 



