DESCRIPTIVE REMARKS. ix 
vid’s, and Longmynd, 
Grits, Conglomerates, and 
Slates. 
CAMBRIAN . + . . Howth, Co. Dublin; Bray 
Head, &ec., in Wicklow ; 
and Forth Mountain, &c., 
in Wexford; Grits, Sand- 
L | stones, and Slates. 
| Harlech, Lianberis, St. Da- 
| 
Fossi_s OF THE CAMBRIAN ROCKs. 
The Cambrian Formation, as described by Sir Roderick Murchison, 
in the ‘ Silurian System,’ is shown to underlie the whole Silurian strata. 
Professor A. C. Ramsay, in his Memoir on the Geology of North 
Wales,* enumerates six districts in which these rocks occur. First, 
that of Anglesea; the strata being mostly composed of mica and chlo- 
rite schists, gneissic rocks, grits, and quartz rock. 
Second. The Bangor and Llanberis district, comprising the altered 
purple, green, and chloritic slates, sandstones, and conglomerate beds ; 
west and south-west of Bangor, together with the purple and green 
slates, and grits on the banks of the Ogwen, around Bethesda, the 
Lakes of Llanberis, &c. 
Third, The Lleyn district, consisting of schist rocks on the south 
side of Caernarvon Bay, &c., including Bardsey Island, and the coast from 
Bardsey Sound to Porth Nevin. 
Fourth. The Harlech district between the Barmouth estuary and 
that of Traeth-bach, principally composed of greenish grits, occasion- 
ally interstratified with green and purple slates. 
Fifth. The district of St. David’s, comprising the purple sandstones 
and slates on the north side of St. Bride’s Bay, in Pembrokeshire. 
Sixth. The Longmynds and the neighbourhood of Shrewsbury, in 
Shropshire, consisting of purple and green grits, conglomerates and 
slaty beds. 
No certain evidence of organic remains has yet been found in these 
rocks in Wales, except in the Bangor slate quarries, by Mr. J. W. 
Salter, who has described what he believes to be the filled-up burrows 
of marine worms, referred by him to Chondrites.| That paleontologist 
also alludes to the discovery of abundant traces of former life in some 
of the fine-grained sandstones and shales composing the strata of the 
Longmynds.{ He described them, as consisting principally of the 
* Memoirs of the Geological Survey of Great Britain (1866), pp. 8, 9, &e. 
+ Mem. Geol. Survey, vol. iii., Appendix, p. 243 ; woodcut, fig. 1. 
t Journal of the Geological Society, vol. xii., p. 248 (1856); and vol. xili., p. 206 
(1857). 
b 
