2 Sir R. I. Murchison’s Address on the 
rande (the lower Lingula flags of Britain) is largely represented 
in North America, however it may occupy an inverted position 
in some cases, and in others be altered into crystalline rocks. 
In determining this question due regard has been had to the 
great convulsions, inversions, and breaks, to which these ancient 
rocks of North America have been subjected, as described by 
Professors Henry D, and W. B. Rogers. 
nan able review of this subject, Mr. T. Sterry Hunt thus ex- 
presses himself:—“ We regard the whole Quebec group, with its 
underlying primordial shales, as the greatly developed represen- 
tatives of the Potsdam and Calciferous groups (with part of that 
of the Chazy), and the true base of the Silurian system.” “The 
Quebec group with its underlying shales,” this author adds (and 
he expresses the opinion of Sir W. E. Logan), “is no other than 
the Taconic system of Emmons;” which is thus, by these authors, 
as well as Mr. James Hall, shown to be the natural base of the 
Silurian rocks in America, as Barrande and De Verneuil have 
proved it to be on the continent of Europe. 
zone of Bohemia. In North Wales that zone has hitherto been 
mainly characterized by Lingula and the crustaceans Olenus and 
Paradoxides. Certain additions having been made to these fos- 
sils, Mr. Salter finds that of the whole there are five genera 
peculiar to the lower zone, and seven which pass upwards from 
it into the next overlying band or the Tremadoc slate. But 
the overlying Tremadoe slate, hitherto also grouped with the 
Lingula flags, is, through its numerous fossils (many of them 
of recent discovery), demonstrated to constitute a true lower 
member of the Llandeilo formation. For, among the trilobites, 
the well known Llandeilo forms of Asaphus and Ogygia range 
