OF RHYMNEY AND PEN-Y-LAN, CARDIFF. 507 
rings appear in thin slices of the limestone lying above the Rhymney 
grit. ‘Transy. sect. from Wenlock limestone, Cae Castell. (x 30.) 
Fig. 27. Fragment of the shell of a Brachiopod, its angles having been rounded 
off, its surface enveloped and its canals infiltrated with dark-brown 
iron oxide. Transv. sect., from Wenlock limestone. (x 380.) 
28. Section of a Foraminifer infiltrated with greenish silicate from lime- 
stone above the Rhymney grit. (xX 50.) 
29. Ferruginous granule enclosing a disk of an Encrinital stem, which had 
been infiltrated by dark-brown iron oxide. ‘Transv., sect., Wenlock 
limestone, Cae Castell. (x 50.) 
Discussion. 
The Prustpent confirmed the views of the author as to the non- 
organic origin of the Cornstones, and that a few limestones are to 
some extent of mechanical origin and derived from older limestones. 
Prof. Ramsay spoke of the difficulty of getting the corrections 
made by the Geological Survey engraved on the Ordnance Maps. 
The original mapping was done as long ago as 1842, but has since 
been corrected ; and the Upper Silurian strata of the region described 
by Mr. Sollas have been added to the Map. 
Mr. Braxe confirmed the accuracy of the author’s descriptions 
from his own observation. He stated that in mineral character the 
Upper Silurian and Old Red Sandstone are very similar. 
Mr. Juxus-Browne asked if there was any evidence of any break 
in the Old Red Sandstone. 
Dr. Hicks stated that a species of Pentamerus, of long range, was 
found in the Caradoc, Llandovery, and Wenlock, and therefore that 
it was difficult frequently to assign an exact horizon to some fossils. 
Dr. Duncan could not agree with Dr. Hicks that the Upper 
Silurian and Lower Silurian could not be distinguished from one 
another by their fossils. He thought that the grouping of certain 
forms was quite distinct in the two series. 
Mr. Sottas replied to the President that he was glad to receive 
such important confirmation of his observations; to Prof. Ramsay 
that Mr. Sollas had himself found a fine-grained calcareous marl 
in the gravel-pit of Barnwell, Cambridge, to be composed chiefly 
of coccoliths, which had been derived trom the denudation of the 
Chalk hills of Cambridgeshire, and that calcareous sediment, con- 
sisting of coccoliths, was still in process of mechanical transportation 
by the river Cam; to Mr. Blake that the species of Pentacrinus 
found above the Wenlock limestone, though smaller than the ordi- 
nary P. oblongus, was not smaller than its variety, P. levis, and 
that the red colour of the rocks is to a great extent merely super- 
ficial ; to Dr. Hicks that he agreed with him in thinking that the 
range of seyeral Upper Cambrian species may have to be extended ; 
to Mr. Jukes-Browne that there was no discernible unconformity 
in the Welsh Old Red, and that the overlap near Llandeilo was 
that of the Siluro-Carboniferous series onto the Cambrian and not due 
to an unconformity between the members of the Siluro-Carbonife- 
rous itself; and to Dr. Duncan that he hoped the corals referred to 
by him might receive the attention of one who understood them — 
so well. 
