24 IXTRODLXTIOX 



more uorthern districts, a conclusion whicli has been abundantly, verified 

 by later investigations. 



Murchison and Sedgwdck subsequently visited the lower valley of the 

 Ehine in Germany where they found a far better development of Devonian 

 strata, abounding with the remains of marine life. These beds which they 

 and their successors have shown to be of the same age as the Devonian of 

 England, have become in reality, if not in name, the type of the Devonian 

 System of the world. 



The Sandberger brothers later studied the Devonian of the Rhine in 

 greater detail and showed that it may be divided into three parts which 

 they termed the Lower, Middle, and Upper Devonian. These divisions 

 differ both in their lithology and their contained faunas. The Lower and 

 Upper Devonian consist chiefly of sandstones and shales, -while the Middle 

 Devonian is formed more largely of limestone. 



The limits of the Devonian were not clearly defined by the earlier 

 students. This arose from the conditions in the regions where the sys- 

 tem was first studied. In western England the marine fossiliferous 

 Silurian passes by numerous transition beds into the almost unfossil- 

 iferous red rocks of the Old Eed Sandstone, affording no sharp line of 

 division. In Devonshire also, the base of the Devonian is poorly shown. 

 Hence the relation of the Silurian and Devonian is not well defined 

 in the localities where they were first named. In the Ehine A*" alley the 

 contact of the Silurian and Devonian is also poorly exposed and the 

 Silurian is absent over much of that area. 



There are extensive series of strata, rich in marine fossils, in the Hartz 

 Mountains and in Bohemia that were referred by early students to the 

 Silurian System. The strata of Bohemia are particularly profuse in 

 organic life and have been made famous by Barrande in his great work, 

 " Systeme Silurien du Centre de la Boheme." Keyser, following a sugges- 

 tion of von Beyrich, established the Devonian age of the upper part of the 

 supposed Silurian strata of these regions, basing his correlation upon a 

 detailed comparison of the organic life of the Lower Devonian beds of the 

 Hartz, Bohemia and the Ehine Valley. His general results have remained 

 secure although modified in many details by later workers. 



