OF RHYMNEY AND PEN-Y-LAN, CARDIFF. ~ 505 
I do not doubt, therefore, that the red globules of hematite have 
been derived by oxidation from the spherical concretions of pyrites ; 
and I believe the latter to result from the unhindered crystallization 
round nuclear centres of iron sulphide, resulting from the reduction 
of salts of iron which were diffused in solution throughout the 
limestone before it became consolidated, or through the canals of 
Foraminifera before they had become completely fossilized. 
In concluding the description of the limestone, one may mention 
that on being heated with hydrochloric acid it dissolves, leaving be- ~ 
hind an insoluble gritty mud of a dark greenish colour. Dried and 
mounted in balsam, this mud is found to consist of grains of 
siliceous sand, globules of iron-pyrites, and casts in green silicate 
of minute univalves, Foraminifera, Encrinital skeletons, and the 
canals of Brachiopod shells. The Encrinital casts are very beautiful 
objects, and reproduce the form of the network so perfectly as to 
mislead one at first into regarding them rather as pseudomorphs of 
that network than as casts of its meshes. 
3. Iron Galls in the Ferruginous-mud Bed above the Rhymney Grit.— 
These, when examined in thin slices under the microscope, show a 
dark chocolate-coloured, quite opaque matrix of iron oxide, through 
which are scattered more or less sparingly a number of very minute 
sharply angular fragments of calcite, with here and there a grain 
of quartz. No concentric or radiating structure is visible with 
transmitted light; but with reflected light a faint concentric line of 
darker colour than the general surface can be made out near the 
external edge. A chemical analysis of one of these galls, hastily 
made by Mr. James, of University College, Bristol, gave the follow- 
ing results :— 
WHET CVORACO) Se les cisst oxenies en & sacs 77:6 
Silica, soluble and insoluble .......... 12:9 
Carbomieyan hydra dey gels cees-uy ae ta 1) 2°9 
Calcim; oxidore aki . layne ee 6:6 
° 100-0 
4. Ferruginous Staining of Ludlow Sandstones.—Some of the 
greenish-coloured sandstones of the Lower Ludlow are occasionally 
penetrated by thin strings of a bright red colour, due to the infil- 
tration of red oxide of iron after consolidation ; sometimes the red 
oxide is present in such quantity as to form thin strings, about 4,” 
wide, of fibrous géthite, in which case the adjacent stone is stained 
red for a considerable distance, 3 to 1 inch, on each side of the pure 
mineral. The strict parallelism of the edges of the stained bands to 
the joints and bedding-planes of the sandstone proves the infiltration 
to have been subsequent to the consolidation and jointing of the rock. 
5. Gothite in Bedding-planes of Rocks immediately below the Rhym- 
ney Grit.—In the Rhymney quarry an irregular bed or series of len- 
ticular patches of gothite occurs just below the Grit, close to the thin 
calcareous seam seen here; it is from 1 to 2 inches in thickness, 
very pure, and cavernous in the middle, the surface of the hollows 
being frequently lined by scalenohedra of calcite, or dog-tooth spar. 
