26 UPPER CAMBRIAN. 
earthy slates and limestones which contain, in favourable localities, a distinct fauna. They are directly com- 
parable with the Orthoceratite limestones of Sweden, the Bird’s Eye and Black River limestones of N. America. 
The Moffat group of 8S. Scotland and the wpper Skiddaw slate are part of the series. 
The new term, ‘Middle Bala’ group, is adopted here for the Bala limestone and its associated sandstones 
and slates, several thousand feet thick in N. Wales, but reduced to a minimum in S. Wales, where it appears as 
dark incoherent schist. In Shropshire this series is known as the Caradoc sandstone, with its Horderly lime- 
stone. The ‘Oskarskal’ group of Sweden (Regio VI. Trinucleorum of Prof. Angelin, the ‘Stratum quartum’ of 
Linneus) represents this group. It is the Trenton and Hudson River group of N. America, and the major part 
of Barrande’s great fossil-bearing formation Etage D. belongs to it. (The Coniston limestone: the limestone 
of Kildare: the Craig Head limestone of Ayrshire: the Peebles limestone: all are of this age.) 
‘Upper Bala’ comprehends the Aber Hirnant beds above the Bala limestone, with a peculiar set of fossils: 
the lower portion of the Coniston flag, viz., that conformable to the limestone; and indeed all beds above the 
Bala limestone and beneath the May Hill sandstone. In the Bala and Coniston sections, we do not indeed 
quite reach the horizon of the Llandovery rocks, with their peculiar fauna—Petraia, Atrypa, Pentamerus, &e. 
But the group ‘Upper Bala’ was made to include all the beds, whether near Meifod, or Welchpool, or near Llan- 
wddyn, Montgomeryshire, which lie above the Bala limestone, and wnder the ‘unconformable’ cover of the Denbigh- 
shire grit and flag. 
There is therefore both propriety and symmetry in retaining the name ‘Upper Bala’ for those beds (having 
on the whole a distinct fauna) which lie above the Bala limestone. The group includes, in ascending order— 
(a Hirnant limestone = Coniston flag, the lower part only (Ash Gill; Coldwell, &c.) 
iter and slate (Sedgw.). above the Coniston limestone. Not the Brathay or Horton 
(Sedgwick). eo 
2. Llandovery beds:— So called by Murchison from the locality where they are best 
Phillips, Salter, &e. exhibited. The group has received much illustration of 
(Lower Llandovery, late years. It is the ‘Mathyrafal limestone’ near Meifod, 
Murchison) Medina of Sedgwick. It skirts all the lower border of the Denbigh 
Sandstone, North flags and grits, from a point a few miles S. of Bala to 
America, Builth: and then rising out from under the May Hill 
group at Llandovery, ranges to the sea in Pembrokeshire. 
It is the great fossiliferous group at Haverfordwest. Its parallel in Westmorland has not yet been found*, unless 
part of the Coniston flag (lower) belongs to it. But in S. Scotland it is conspicuous at Dalquorhan and Mullock 
in Ayrshire. In Galway the fossiliferous rocks of Maume and Cong belong in great part to it. [But the Irish 
collection is kept separate, and will be catalogued to follow the British one.] 
N.B. In the list of localities in the Synopsis, p. 326, &c., the terms Upper and Lower Bala are sometimes vaguely used, owing 
to the absence of data at that time for a clear definition of the fossil horizons. It is requested, therefore, that the student will 
consider all the Bala groups of the Synopsis as one, and consult the collection for their division into the modern groups. 
For the placing of many of the fossils under these special geological subdivisions, I am alone responsible. But having studied 
N. Wales under Prof. Sedgwick, 8. Wales under Sir H. de la Beche, and having been engaged for seventeen years working at the 
Silurian and Cambrian fossils of the Geological Survey, Prof. Sedgwick trusts me to arrange them according to the present state 
of our knowledge, 1867. The Bala group or Upper Cambrian of Sedgwick therefore consists of— 
UPPER Lower Bala = Llandeilo flag (Upper Llandeilo, Geol. Survey, the Arenig being the lower). 
Camprian. } Middle Bala = Caradoc sandstone, and Bala rocks (Geol. Survey and Sir R. I. Murchison). 
(Sedgw.) Upper Bala = Caradoc shales, Hirnant limestone, and Lower Llandovery rock (Geol. Survey). 
All these are unconformably overlaid by the ‘May Hill Sandstone’ or Clinton group, which forms the base of the Silurian 
(Sedgwick) or Upper Silurian (Murchison). 
* Mr. T. McK. Hughes has lately found the equivalents of the Llandovery rock near Coniston, &¢e. It consists of mudstone, conglomerate, 
and beds of Graptolites like those of Barrande’s Etage E. 1, which surely, for many reasons, is a Llandovery group. J.W.S. 
