MIDDLE BALA GROUP. 39 
Mippite Bata Group. Arenaceous rocks and slates (volcanic grits and schaalsteins, with beds of felstone 
porphyry (Snowdon, Moel Hebog, &c.). 
Extent of the group. Prof. Sedgwick only includes in this group the 9000 feet of beds, chiefly arenaceous, 
slaty, and with some calcareous bands, which lie over the dark earthy slates of the Arenig section (Lower 
Bala). The group extends a short distance, probably a couple of hundred feet, above the Bala limestone. 
But it does not include the Hirnant limestone, which is the base of the Upper Bala group next described. It 
appears to represent in mass the whole of the Caradoc Sandstone proper, in Shropshire. 
Organisms. The Hudson River group of New York—the Utica Slate and Trenton limestones—are parallel 
to this large British group. In Sweden, Region D. of Angelin. In Bohemia, Etage D. 3, 4, 5. This group 
is the richest in organic life of all the groups beneath the Old Red Sandstone, not excepting the Wenlock. 
Most of the orders of invertebrata have been found in it; but the supposed remains of fish have proved 
mythical No Hurypteride among the Crustacea, have yet been found. But Trilobites reach their maximum 
here, both as to genera and species (see Mon. Brit, Tril. 1864, Introduction, p. 8). Brachiopods are various and 
innumerable. Corals, Cystidez, and Crinoids are also plentiful, though not of many species, except as regards the 
Cystideew. These attain their maximum here in Britain. Sponges; cup and millepore corals; starfish of several 
species; tubicolar and naked Annelida; Entomostraca—are all common. Mollusca of all orders (except naked 
Cephalopods)—the Heteropods and Pteropods being of giant size. The bivalve shells (Lamellibranchs) are 
allied to Modiola, Arca, and Avicula: (see Phillips, Mem. Geol. Surv. Vol. 1. Pt. 1, p. 264). 



Case and Reference to McCov’s 
Column of 
: ; Names and References; Observations, &c. Numbers and Localities. 
Drawers. Synopsis: and Figures of Genera. 


Zoophyta? or Bryozoa. GRAPTOLITIDZ. 
I think these are Bryozoa (Mem. Geol. Surv. 
Vol. ur. Appendix, p. 328), but arrange them 
in the order of the Synopsis, as their syste- 
matic position is somewhat doubtful. 



Gk7 G. Ludensis. Graptolites priodon, Bronn (@. /udensis, Murch. | Grieston, Peebleshire. 
p: 4. Siluria, 2nd ed. p. 64, t. 12, fig. 1). The | Penarth uchaf, N.W. of 
finest specimens of this long-lived fossil are | Pen-y-glog. 
from rocks of this group in Scotland. 

Gk? p. 5. Graptolites sagittarius, Hisinger, (not Linn.) Horton, Ribblesdale; Ro- 
Leth. Sue. t. 35, fig.6. Salter, Siluria, 2nd | ther Bridge, Studgill 
ed. p. 542, Quart. Journ. Geol. Soc. VIL p.390. 
(G. Hisingeri, Carr. Geol. Mag. v. p. 126.) 
Gk? p. 6, Pl. 1s, f 2. Graptolites Sedgwicki, Portl. (Siluria, 2nd ed. | Grieston, on the Tweed. 
Foss. 11, fig. 2). A common species in the 
Tyrone and Fermanagh schists of Ireland, 
which are most probably of this age. 
Gk? Graptolites, sp. with very narrow cells. Bala. (J. Peters, Esq.) 
Gk? p.G, Pll, tidy 5: Graptolites tenuis, Portl. Geol. Rep. p. 319, t. 22, Grieston, on the Tweed. 
f.6. (Siluria, 2nd ed, p. 55, Foss. 10, fig. 12.) 
