OF RHYMNEY AND PEN-Y-LAN, CARDIFF. 483, 
had previously presented; and I was subsequently able to trace the 
Rhymney bed right across the Pen-y-lan district to the Starting- 
house on Heath-farm hill. It forms a well-marked feature in the 
country ; and quarries have been opened in it at half-a-dozen places 
along its outcrop. 
In one of these quarries, which occurs just on the edge of Coed- 
tir-Caled, Mr. Ross and I observed false-bedding as perfectly dis- 
played as by many glacial sands. 
Several of the joint-planes in this quarry were polished and striated 
with true slickensides; but no trace of a fault could be found. It is 
true that the joint-face was coated with hematite, and that the 
striation might be attributed to a fibrous structure in this mineral ; 
but such is not the appearance it has to my eye, and I prefer to 
believe that it resulted from movements among the already jointed 
rocks, which took place when the Siluro-Carboniferous country was 
being elevated above the sea-level. 
We may now conveniently resume our description of the river 
section exposed on the side of Cae Castell, and further north. 
River Section.— Above the Rhymney Grit, which we mentioned as 
occurring at the base of this section, a series of alternating argilla- 
ceous and sandstone beds succeeds, to a great extent mud-covered 
and of no great interest, till at a distance of 107 feet vertically above 
the Rhymney bed we reach a curious reddish-brown ferruginous 
mudstone, thickly crowded with a number of irregular concretions or 
galls, and containing fossils. It is, however, so very badly exposed 
that I only succeeded in obtaining a single specimen of the latter, which 
is a well-marked Grammysia cingulata. This bed is followed for 
11 feet 4 inches by alternating compact flaggy, argillaceous, and 
siliceous sandstones of a greenish and yellowish-grey colour. A blue 
erystalline bed of limestone then appears; it is 5 inches thick, and 
is composed of a number of crushed fossils—Rhynchonella, Orthis, 
Strophomena, and Encrinite-fragments too imperfect for specific 
identification. Above this, compact siliceous sandstones, flaggy 
argillaceous sandstones, and mudstones follow for 8 feet vertically, 
and then more or less broken ground for about 50 feet vertically, 
when we reach the following section, which is very clearly exposed 
in the side of Cae Castell :— 
Section im the side of Cae Castell (ascending order). 
1. Alternations of flagey fossiliferous and compact siliceous sand- ft. in. 
stones, of greenish-grey colour, generally micaceous ............ 5 2 
2. Grey compact sandstone bed, more or less calcareous .............46 0 10 
By, Liha! Cit Inia) so46do00e0 deeodoosbanodoc0bodo0aD 6D odHOo0G0qDDNe0K00G0006 0 2 
4, Blagey grey siliceous sandstone -......0.....ccscececceceeecceoneecsceeeves 1 8 
5, Hard grey siliceous limestone, weathering yellowish brown ...... 1G 
6. Siliceous sandstone, with an intercalated band of limestone 1 inch 
BIC eaters tateice setiactve soa certe cise ed's aaalsuie wisi ciutelanlcles site bisaaatits mieina gave 4 
7. Parting of yellowish calcareous and fossiliferous sandstone......... 0 2 
8. Caleareous fossiliferous sandstone ; light bluish grey, weathering 
pV Gllowigeresemecotacemats ons ates secure seiatskiaicisniciriae sosidenl seems nh salteetaseee 2 
9. Yellowish and greenish-grey shales — ............seceecsecscescsvenaneaee 0 6 
10. Light-grey crystalline limestone, fall of corals .........cceseeeeeeneene 0 6 
Carley LOLWALC Maccnoiernsshavsssoatsoresastnaesaeemeeemeae manete 14 0 
