144 OBSERVATIONS ON THE 
upper part of the system. The massive red and brown sand 
stones which form the Carmarthenshire Van rest on the quartz 
conglomerate of Cwm Sidan, and this I take to be the base of 
the Devonian of that area. Below the conglomerate come the 
red shales of the Sawdde, which I hold should be cut off from 
the Devonian and bracketed with the Silurian. They have, as 
I believe, no representatives either in Devonshire or in the 
northern sections C, D, E. For them I have proposed the. 
name Merthynian, from the county where they are best seen. 
These pass down rapidly into the flaggy sandstones of the top 
of the Ludlow, which are locally called Tilestones, as in 
that district they were used for roofing most of the old 
churches and farms. But from their weight they required too 
much timber, and therefore slates have now been generally 
introduced instead of them. They are well seen by the Black 
Cock old coaching inn, and in many other places along the 
borders of Carmarthenshire. Below them is a massive sandy 
rock much used as a building stone and known as Hay Sand- 
stone from a town of that name on the borders of Breconshire. 
From beneath these sandy upper beds the main mass of shaley 
Ludlow crops out, and, being of great thickness, forms a 
considerable feature. 
At Cae Sara, near Myddfai, between the Towy Valley and 
the Black Mountains, a limestone occurs of sufficient importance 
to be burnt for lime, and this is identified on palzontological 
evidence with the Wenlock Limestone. Where this limestone 
is not seen there is nothing to fix the exact boundary between 
the shale above, which is correlated with the Ludlow, and the 
shale below, which is referred to the Wenlock. Where, how- 
ever, a large number of fossils can be obtained /rom one bed 
there is generally a sufficient difference in the facies to enable 
us to refer the shale to one or the other. 
Between the Wenlock and the May Hill Sandstone there 
is mostly a series of fine shales of a red or yellowish-grey paste 
colour, or red passing down into pale shale, and this into dark 
lead-grey shale. Very few fossils have been recorded from 
this series in Carmarthenshire. It is well exposed in the 
Valley between Epynt and the celebrated locality for May Hill 
fossils, Craigyrwyddon. . 
The May Hill Sandstone of this areais very fossiliferous. Itmay 
be divided roughly into three horizons, the Upper which passes 
up into the Wenlock Shale and is characterised by Pen‘amerus 
oblongus; this is well seen at Castell Craig-yr-Wyddon. The 
Middle which is characterised by the occurrence of Sérick- 
landinia lens as well as Pentamerus oblongus, and is seen 
about Pant-y-gaseg, near Llandovery; and the Lower in which 
Meristella crassa occurs with Svtricklandinia lens, but no 
Pentamerus oblongus. This may be traced from North of 
Craig-yr-wyddon, S. West, to the Towy, and on the other side of 
