LOWER BALA GROUP. 
bo 
or 
UppreR CamBriaAN (Cambro-Silurian of some authors; Lower Silurian of Murchison; &c.). 
As there has been much controversy respecting the name to be borne by the rocks overlying the primordial 
or “Ffestiniog” group, and underlying the “ May Hill Sandstone;” a table of equivalents is here added, which 
may serve to guide students to the cases, and harmonize the modern text-books with the ‘Synopsis’ pub- 
lished in 1851-2 by Prof. Sedgwick and McCoy, which is the basis of this Catalogue. 
Sir R. I. Murcurson. 
1831—1859. 
Llandovery rocks, in 
1859. 
Caradoc Sandstone 
and 
Llandeilo flags 
(Lower Silurian). 
Lingula flags (base 
of Lower Silurian). 
Cambrian, or Long- 
mynd rocks. 
Sir H. pr 1a Brcue, 
and Grou. Surv. 
1840—1866. 
Pror. Prinuies. 
1855. 
BarranveE, to 1860. 
Sir W. Locan and 
E. Bruiryes, to 1866. 
J. W. Sauter, 
1864—1866-9., 
SEDGWICE. 
1832—1853. 

Upper Caradoc, or 
Upper Llandovery 
(Upper Silurian). 
Lower Llandovery. 
Caradoc or Bala. 
Llandeilo. 
Lower Llandeilo. 
Tremadoc. 
Lingula Beds. 
Cambrian. 

Wenlock. 
May Hill. 
Llandovery. 
Caradoe or Bala. 
Llandeilo. 
Tremadoc. 
Ffestiniog Group. 
Etage E. base. 
Etage D. 5. 
Etage D. 4. 
Etage D. 3. 
Etage D. 2. 
Etage D. 1. 
Blank here, not no- 
ticed by M. Barrande. 
tage C. 
Harlech and Bangor | Etage B. 
Group. 

Clinton Group. 
Anticosti Group. 
Hudson River Gr. 
Trenton Group. 
Black River Group. 
Bird’s Eye Group. 
Quebee Group. 
Chazy Group. 
Potsdam Group. 
St John’s Group. 
Huronian, 

Upper Wenlock. 
Lower Wenlock. 
May Hill Group. 
Llandovery Group. 
Caradoc or Bala 
Group. 
Llandeilo Group. 
Arenig or Skiddaw 
Group. 
Upper 
Tower Tremadoc. 
Upper ) Ffestiniog 
Middle Group. 
Menevian Group. 
Harlech Group. 
Longmynd Group. 
Upper CamBrian (Lower Bala Group: Middle Bala: Upper Bala). 

Wenlock Group. 
Denbigh flag. 
May Hill Sandstone. 
Upper Bala. 
Lower Bala. 
Arenig Group. 
Tremadoc Group. 
Ffestiniog Group. 
Harlech Group. 
Longmynd Group. 
The ‘Lower Bala’ of the Synopsis (Introd. p. xx.) was made to include the dark earthy slates, with 
occasional bands of limestone, such as are exhibited on the east flank of the Arenig range; the Mynydd 
Tarw and Craig-y-glyn above Llanarmon, in the Berwyn Mountains, and the black slates about Bangor and the 
flanks of Snowdon. 
limestone, and that limestone itself. 
Further research, however, by the Geological Survey has shewn that these dark earthy slates, with 
occasional limestone, are the equivalent of the black slates and limestones of 8. Wales, collectively known as the 
Llandeilo flag in its modern signification *. 
It also comprehended the arenaceous deposits on the W. side of Bala lake, below the Bala 
Prof. Sedgwick therefore permits me to restrict the term to the 
* The original ‘Llandeilo flag’ comprehended much more, and many higher beds, of different ages; and could not, at the time of the 
It is much better understood now. 
publication of the ‘Synopsis,’ be at all accurately identified. 
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