ioo Devonian Strata. 



opinion, that the Devonian strata are in the main the 

 'marine equivalents of the Old Red Sandstone, continues 

 to be generally held. Till a new survey of Devonshire 

 helps to settle the question I give the usual reading of 

 the history of the Devonian strata^ though I think it 

 probable that Jukes will turn out to be correct in 

 questioning the right of the Devonian strata to the 

 conventional name of an independent series. 



In Devonshire the strata have been divided into 

 Lower ; Middle, and Upper Devonian. The Lower 

 chiefly consists of slaty beds and green and purple 

 sandstones, with many Brachiopoda of the genera 

 Chonetes, Orthis, Spirifera, &c. The Middle group, 

 which includes the Plymouth limestone, contains 

 numerous corals, the most common genera of which are 

 Acervularia, Alveolites, Cyathophyllum, Favosites, 

 Petraia, Strephodes, and the sponge Stromatopora. 

 With these are found Encrinites, Spirifers, Atrypce, 

 Leptcence, Productce, RhyncTionellce^ Stringocephali., 

 and Calceola (G. sandalina) the last a genus peculiar 

 to the Devonian rocks. Many Lamellibranchiate mol- 

 luscs also occur, together with Gasteropoda of the genera 

 Euomphalus, Loxonema, Machrocheilus, Murchisonia, 

 Pleurotomaria, Turbo, &c. Also many Cephalopoda 

 of the genera Clymenia, Cyrtoceras, Orthoceras, 

 Goniatites and Nautilus. The last two are unknown 

 in the British Silurian series, though Nautilus occurs 

 in the Upper Silurian rocks of North America. The 

 Groniatite may be roughly said to be intermediate in 

 structure between the Nautilus and Ammonite. The 

 latter does not occur in Palaeozoic strata. A few 

 Trilobites are found in the British Devonian rocks, and 

 various Crinoids. The Upper Devonian group contains 

 land plants and many shells, some of which are 



