XV.] CAMBRIAN AND SILURIAN IN NORTH AMERICA. 423 



Lower and Middle Cambrian divisions of Sedgwick, which 

 the latter had separated from the Upper Cambrian on strati- 

 graphical grounds, and which were subsequently found to 

 contain a distinct and more ancient fauna. 



The name of Silurian should therefore be restricted, as 

 maintained by Sedgwick and by the Messrs. Eogers, to the 

 rocks of the third fauna, the so-called Upper Silurian of Mur- 

 chison ; and the names of Middle Silurian, Lower Silurian, 

 and Primordial Silurian banished from our nomenclature. 

 The Cambrian of Sedgwick, however, includes the rocks both 

 of the first and second faunas. To the former of these, the 

 lower and middle divisions of the Cambrian (the Bangor and 

 Festiniog groups of Sedgwick), Phillips, Lyell, Davidson, 

 Harkness, Hicks, and other British geologists agree in apply- 

 ing the name of Cambrian. The great Bala group of Sedg- 

 wick, which constitutes his Upper Cambrian, is, however, as 

 distinct from the last as it is from 1)he overlying Silurian, and 

 deserves a not less distinctive name than these two. Its origi- 

 nal designation of Upper Cambrian, given when the zoological 

 importance of Lower and Middle Cambrian was as yet un- 

 known, is not sufficiently characteristic, and the same is to 

 be said of the name of Lower Silurian, wrongly imposed upon 

 it. The importance of this great Bala group in Britain, and 

 of its North American equivalent, the Matinal of Eogers, 

 including the whole of the limestones of the Trenton group, 

 with the succeeding Utica and Hudson Eiver shales, might 

 justify the invention of a new and special name. That of 

 Cambro-Silurian, at one time proposed by Sedgwick himself, 

 and adopted by Phillips and by Jukes, was subsequently with- 

 drawn by him, when investigations made it clear that this 

 group had been wrongly united with the Silurian by Murchi- 

 son. Deference to Sedgwick should therefore prevent us from 

 restoring this name, which, moreover, from its composition, 

 connects the group rather with the Silurian than the Cambrian. 

 Neither of these objections can be urged against the similarly 

 constructed term of Siluro-Cambrian, which, moreover, has the 

 advantage that no other new name could possess, of connect- 



