194 STRATIGRAPHICAL GEOLOGY 



The Devonian System was established by Sedgwick and Murchison 

 in. 1839 because they found in Devon a great series of rocks 

 containing a special assemblage of fossils, and they divided this 

 Devonian System into Lower, Middle, and Upper Groups ; the 

 convenience of this division has been confirmed by the researches 

 of continental geologists. 



Sedgwick and Murchison also took a leading part in the investi- 

 gation of the European equivalents of these Devonian rocks, visiting 

 the Rhenish mountains and indicating the existence of rocks con- 

 taining a Devonian fauna in the Eifel district (1842). The more 

 complete delimitation of the Devonian System was accomplished 

 by F. Rb'mer (1844), Von Dechen (1855), and the Sandbergers 

 (1850-56). A little later came the important researches of Gosselet 

 on the rocks of the Ardennes (borders of France and Belgium), 

 where he established the same order of succession. 



The Old Red Sandstone, which elsewhere occupies the position 

 of the Devonian System, is believed to be of lacustrine or estuarine 

 origin. It has been divided into a lower and upper series, with 

 a middle series in Wales, but in Scotland there is a marked uncon- 

 formity between the upper and lower series, and some are doubtful 

 whether the upper series is really of Devonian age. It is 

 probable that the Lower Old Red Sandstone may be correlated 

 with the Lower Devonian, that the Middle Devonian was formed 

 during the time represented by the unconformity in Scotland and 

 Ireland, but how much of the Upper Old Red Sandstone is really 

 of Devonian age will depend very largely on the results of further 

 researches in North Devon and Ireland. 



In dealing with the records of the Devonian period we shall 

 describe the marine facies first, both in England and on the conti- 

 nent, and secondly the rocks known as the Old Red Sandstone. 



I. THE DEVONIAN FACIES 

 A. THE MARINE FAUNA 



As already mentioned, the Devonian fauna is intermediate in 

 character between those of the Silurian and Carboniferous. Most 

 of the characteristic Silurian genera become extinct in the Lower 

 and Middle Devonian, while in the Middle and the Upper 

 Devonian many genera which are prominent members of the 

 Carboniferous fauna make their appearance. This is especially 

 the case with the Brachiopoda, for all the Lower Devonian genera 

 are found in the Silurian, while all those in the Upper Devonian 

 range into the Carboniferous. 

 ' The following is a brief account of the principal genera which 



