Charles Schuchert — Historical Geology, 1818-1918. 81 



in England, and it is to Sedgwick's credit that he was the 

 first to point out this fact and also the presence of an 

 unconformity. It therefore follows that we cannot con- 

 tinue to use Silurian system in the sense proposed by 

 Murchison, since it includes two distinct systems or 

 periods. Dana, in the last edition of his Manual of 

 Geology (1895), also recognizes two systems, but 

 curiously he saw nothing incongruous in calling them 

 4 'Lower Silurian era" and "Upper Silurian era." It 

 certainly is not conducive to clear thinking, however, to 

 refer to two systems by the one name of Silurian and to 

 speak of them individually as Lower and Upper Silurian, 

 thus giving the impression that the two systems are but 

 parts of one — the Silurian. Each one of the parts has its 

 independent faunal and physical characters. 



We must digress a little here and note the work of 

 Joachim Barrande (1799-1883) in Bohemia. In 1846 he 

 published a short account of the " Silurian system" of 

 Bohemia, dividing it into etages lettered C to H. 

 Between 1852 and 1883 he issued his "Systeme Silurien 

 du Centre de la Boheme," in eighteen quarto volumes 

 with 5568 pages of text and 798 plates of fossils — a mon- 

 umental work unrivalled in paleontology. In the first 

 volume the geology of Bohemia is set forth, and here we 

 see that etages A and B are Azoic or pre-Cambrian, and 

 C to H make up his Silurian system. Etage C has his 

 1 1 p r i m ordial fauna, ' ' now known to be of Paradoxides or 

 Middle Cambrian time, while D is Lower Silurian, E is 

 Upper Silurian, F is Lower Devonian, and G and H are 

 Middle Devonian. From this it appears that Barrande 's 

 Silurian system is far more extensive than that of Murchi- 

 son, embracing twice as many periods as that of England 

 and Wales. 



About 1879 there was in England a nearly general 

 agreement that Cambrian should embrace Barrande 's 

 Primordial or Paradoxides faunas, and in the North 

 Wales area be continued up to the top of the Tremadoc 

 slates. -To-day we would include Middle and Upper 

 Cambrian. Lower Cambrian in the sense of containing 

 the Olenellus faunas was then unknown in Great Britain. 



Lapworth, recognizing the distinctness of the Lower 

 Silurian as a system, proposed in 1879 to recognize it as 

 such, and named it Ordovician, restricting Silurian to 

 Murchison 's Upper Silurian. This term has not been 



