248 J. E. Marr — Cambrian and Silurian Rochs. 



intermediate between M. Barrande's first two faunas, especially after 

 the light thrown upon the fossils of this group by Dr. Linnarsson 

 (Geol. Mag. Decade 11. Vol. V. p. 188). 



The Tremadoc group is considered by M. Barrande as appertaining 

 from its base to his second fauna. He states that unfortunately 

 some English geologists have associated it with part of the true 

 primordial fauna, in the subdivision which they name Upper 

 Cambrian. If we analyze the list of Tremadoc fossils given in 

 Salter's Catalogue of Cambrian and Silurian Fossils in the Wood- 

 wardian Museum, we find that of eleven genera, two are peculiar 

 to the Tremadoc beds, one occurs both above and below, two occur 

 heloio only, and six above only. This seems to bear out M. Barrande's 

 view of the relation of this formation. Consequently those English 

 geologists who have a tripartite division at present, ought to have 

 a quadripartite one, or at any rate to shift their boundary-line in 

 one case. But, indeed, we can draw hard palseontological lines 

 between most of the groups of the so-called primordial beds in 

 Britain, and I think that the explanation of this is evident. The 

 primordial fauna of Bohemia is the representative of only one 

 English formation, viz. the Menevian ; when the so-called primordial 

 group in Britain has been searched for fossils as carefully and 

 persistently as that part of it in Bohemia which is fossiliferous, these 

 breaks will disappear. In England our opportunities of collecting 

 fossils are rarer than are those of foreign geologists ; consequently 

 we show a preference for working out the richer zones, and do not 

 give so much time as would be desirable to the more barren inter- 

 mediate beds. 



Proceeding to consider the boundary between his second and third 

 faunas, M. Barrande says that in the Llandovery group of England, 

 which has been well studied, the inferior portion contains principally 

 species of the second fauna, whilst the superior holds a majority of 

 species of the third fauna. Our geologists now, however, usually 

 group the Llandovery or May Hill Group entirely with the beds 

 containing the upper fauna, whilst so far is our knowledge of these 

 rocks from being complete, that there is still a great deal of con- 

 fusion as to certain beds, whether they are of Upper Bala age, or 

 belong to the lower part of the May Hill beds. I have in a recent 

 paper (Q.J.G.S. 1880, p. 591) endeavoured to show that M. Barrande's 

 " Colonies," which he appeals to as affording a mixture of the 

 organisms of his second and third faunas, are to be explained as 

 due entirely to physical disturbances. 



M. Barrande states that Murchison's nomenclature is adopted by 

 the Geological Society of London with the consent of nearly all 

 European geologists, and that the names " Primordial Silurian," 

 "Lower Silurian," and "Upper Silurian," are employed in the last 

 edition of " Siluria," a classic work which is in the hands of all 

 geologists upon both continents. The amount of agreement with 

 regard to this classification is shown in the following table, partly 

 compiled from the list in Salter's Catalogue of Cambrian and Silurian 

 Fossils in the Woodwardian Museum : 



