CLASSIFICATION OF PALAEOZOIC ROCKS OF THE BRITISH ISLES. 297 
clearly divisible — at St. David’s, where it has been chiefly ex- 
plored of late years — into three groups. These are called in 
ascending order by the local names of Caerfai, Solva, and 
Menevian [c, cl, e, in Sections and Plates). 
The Caerfai group consists chiefly of conglomerates, sand- 
stones, and red, purple, and green slates and shales. Remains 
of animal life are found throughout. The most important of 
these were discovered by me, in 1868, in red slates, near the base, 
and consist of a IAngulella, Piscina , Leper clitia, a doubtful head 
of a trilobite, and abundant traces of annelids. 
Beds of the same age are also found in the Harlech Moun- 
tains. The great slate quarries of Llanberis, Bethesda, and 
other places in Caernarvonshire, are also on this horizon. 
Though the basal beds are not exposed in the Longmynd area, 
it is probable also that some belonging to this group occur 
there. There is a strong general resemblance between the 
beds of this group in each of the areas, but as they were at 
first shore-deposits around a subsiding land-area, some dif- 
ferences in appearance and in thickness must necessarily occur. 
The great conglomerates which rest on the Eozoic rocks along 
the north-west coast of Scotland, are supposed to be of Lower 
Cambrian age, and may possibly be to some extent contempo- 
raneous deposits with the beds of this lower group at St. David’s. 
This group may be conveniently divided into three parts as 
under : — 
j- Purple Sandstones with Annelids , &c. 
j Red Shales and Schists, with Leperditia cambrensis, Lin- 
) gulella primceva, Discina caerfaiensis, &c. 
( Conglomerates and Greenish Flaggy Sandstones with 
j Annelids, Fucoids, &c. 
Solva group . — Like the underlying Caerfai group, this may be 
also divided into three parts. The lowest beds are yellowish 
sandstones, with some conglomerates, and these are succeeded by 
grey flags. The latter contain an important fauna which I dis- 
covered in 1867. It consists of several trilobites, including 
the genera Plutonia, Paradoxid.es, Conocoryphe, and Micro- 
discus, also a Lingulella, Theca, and Protospongia. The species 
are all restricted to this horizon, and the genus Plutonia has 
not been discovered elsewhere as yet. The middle portion 
of this group consists of red, purple, and grey grits, sandstones, 
and slates ; it is of great thickness, and probably contains 
several fossiliferous horizons. At present, though fragments 
have been found in several different beds, the only position 
in which they appear to occur in any abundance, is towards 
Ph* 
Upper, 
P 
o 
1000 ft. 
Ph 
Middle, 
3 \ 
50 ft. 
pH 
Ph 
m 
Lower, 
o 
l 520 ft. 
