OF RHYMNEY AND PEN-Y-LAN, CARDIFF. 485 
The previously ascertained range of each species is shown in the 
vertical columns appended to the list, which on mere inspection will 
convince us of the age of the beds in which the fossils occur. No 
one I think will hesitate to refer this forty feet or so of the Cae 
Castell section to the horizon of the Wenlock limestone, although 
the total thickness of true limestone beds which occur in it does not 
exceed a foot or two at the most. If this determination be accepted, 
then the occurrence of bed 19 about 16 feet above the layer of 
Wenlock corals is somewhat surprising, since the higher bed is 
crammed with casts of true Pentamerus oblonqus, var. levis. From 
the imperfect casts I submitted to Mr. Etheridge he concluded that 
they probably represented this species; and on sending them to 
Mr. Davidson he concurred in the opinion of Mr. Etheridge. I 
have since, however, taken impressions in gutta-percha of some of 
the best-preserved of the casts; and these convert the probability 
into a certainty; so that the range of Pentamerus oblonqus, var. 
levis, must, in our district at least, be carried considerably above 
the Llandovery beds and into the middle of the Wenlock. Perhaps, 
indeed, it ranges still higher; for I find in our museum a solitary 
specimen bearing the label Pentamerus levis, and imbedded in 
Aymestry limestone. Above the section just described Silurian beds 
are exposed almost uninterruptedly for about 150 feet vertically. 
I took the trouble to measure and describe every separate bed for a 
thickness of over 100 feet; in this thickness there are 230 separate 
beds, varying from 1 inch to 2 feet 6 inches in thickness. They 
consist of alternations of compact fine-grained sandstones, more or 
less argillaceous thin flaggy sandstones, mudstones and shales, with 
now and then a thin parting of soapy unctuous clay. The prevail- 
ing tints are various shades of greyish green, weathering reddish 
brown, with here and there a bed of red or claret-colour. Many of 
the beds are micaceous ; some abound in fossils ; and others are quite 
devoid of them. ‘There is no connexion between the colour of the 
bed and the presence or absence of fossils, the reddish beds contain- 
ing fossils quite as frequently as the greyish ones. Worm-tracks 
and fucoidal markings are abundant; and many of the beds are 
rippled on the surface. Calcareous matter is rare, only one band of 
impure limstone occurring throughout the series; and that is but 4 
inches thick. It appears 100 feet above the base of this section or 
the top of the preceding one. 
The following is a list of the fossils from this section :— 
