R. G. Carruthers—Corat Zones in Carboniferous Limestone. 171 
the much greater size and abundance of the phenocrysts of uralite, 
hornblende, and orthoclase, and in its coarser texture; the individuals 
may be as much as 1 inch in length. The rock is composed. of 
orthoclase, plagioclase, hornblende, uralite, chlorite, magnetite, 
calcite, and pyrites. Orthoclase is found in large amount both in 
phenocrysts and in the ground-mass. In the former it often shows 
a clearly marked arrangement of concentric zones on the external 
margin of the crystal; the orthoclase is usually cloudy, owing to the 
presence of calcite. Plagioclase is present sometimes, but never to 
such an extent as the orthoclase; it is confined to the ground-mass, 
where it occurs as lath-shaped albite twins, probably andesine. 
Hornblende, like the orthoclase, occurs in two generations, among the 
phenocrysts and in the ground-mass; it is brown and strongly 
pleochroic. The bulk of the coloured constituent of the rock is 
uralite. Magnetite is a decomposition product of the hornblende, 
occurring along the cleavage cracks of the smaller hornblende crystals 
and giving a lattice-like appearance to the mineral. Pyrites may at 
times be very abundant in the rock, but often it is quite absent: it is 
perhaps of secondary origin. 
"It is to be noted that Forbes in 1868 (27) reported and described 
a uralite porphyry from this neighbourhood. 
(Zo be continued in our next Number.) 
V.—On Corat Zones In THE CaRBoNIFEROUS LIMESTONE. 
By R. G. CarruTuErs.! 
MONGST the corals collected by the Geological Survey during 
the past season, and submitted to me for determination, two 
specimens call for special remark, since they appear at first sight to 
occur out of their true zonal position. They were found by Mr. Dixon 
on the Pembrokeshire coast, to the south and south-west of Castle 
Martin. In each case Mr. Dixon gives the horizon as C,—S,, in the 
terms of Dr. Vaughan’s classification. They are, accordingly, of 
Lower Visean age. 
- One of the specimens (K.D. 12538) is referable to the genus Dzbuno- 
phyllum. In cross section there is a general resemblance to the figure 
of Dib. aff.y recently given by Mr. Douglas.? In the Pembrokeshire 
specimen, however, the mesial plate, although conspicuous, is not 
thickened in the middle, and the central area is more clearly separated 
from the septa. In vertical section the central and tabular areas are 
sharply differentiated, the former being crowded with fine vesicles 
directed inwards and upwards at a steep angle. 
The second specimen (E.D. 1350) is an example of Cyathaxonia 
rushiana, Vaugh. A cross section shows the characteristic columella, 
relatively large, oval, and with a ‘lath’ in the centre. 
Hitherto, Dibunophyllum has not been recorded in the British Isles 
below the Dibunophyllum zone (D), while Cyathaxonia rushiana has 
only been found at a still higher horizon in the uppermost Visean, 
1 Communicated by permission of the Director of the Geological Survey. 
2 J. A. Douglas, ‘‘ The Carboniferous Limestone of County Clare”’: Q.J.G.S., 
1909, vol. lxv, pl. xxvii, fig. 6 
