>.< DESCRIPTIVE REMARKS, 
impressions, or surface holes and burrows of marine worms, or Anne- 
lides of two kinds; naming them Arenicolites didymus and sparsus 
(Plate ii., figs. 1, 2); these he supposed to have burrowed in sand, like 
the Arenicola of the present day, having like them entrance and exit 
holes, always in pairs. He also describes what he believed to be a 
Crustacean, as ‘‘ either the caudal shield of a Trilobite, or else a broad 
body segment of a Phyllopod allied to Hymenocaris.”’ 
In Ireland, rocks referred to the Cambrian Formation occur princi- 
pally in three districts on the east coast. First—At Howth, near Dublin, 
extending over but a small area of about two miles; they consist of 
large masses of quartz rock, interstratified with green grits, and green 
and purple slates. Second—That of North Wicklow, commencing a 
little north of the town of Bray, and proceeding south to Wicklow, a 
distance of about seventeen miles, with a breadth of about seven at its 
widest part, including masses of quartz rock, which form the elevated 
peaks of the Great and Little Sugarloaf Mountains. 
There are two small slightly detached districts in North Wicklow ; 
that nearest Dublin at Shankhill, being about one mile anda half long, 
and the third of a mile broad; the other, extending over a greater surface, 
and more important on account of its fossils, is situated near Rathdrum, 
about five miles south-west of Wicklow, being six miles long, and 
nearly a mile broad at its widest part; it also includes masses of 
quartz rock, and forms the eminence called Carrick Mountain. 
The Wexford Cambrian district occupies a considerably larger area 
than either of the others, commencing six miles north of Wexford, 
and terminating four miles east of Waterford Harbour—a length of 
thirty-six miles, with a breadth of about seven at the widest part, near 
Wexford. It includes the Forth Mountain, in South Wexford. 
These rocks consist of a great series of sandstones or gritstones 
and slates, often interstratified with large masses and veins of quartz 
rock.* 
As in the Cambrian rocks of England and Wales, fossils are here rarely 
met with; they were only discovered after great perseverance by the late 
Dr. J. R. Kinahan, on the north shore of the promontory of Howth; and, 
although not very definite, consist of track-like markings on the surfaces 
of some of the compact sandstone beds, which he considered referrible to 
Annelides and Mollusca ; from under these, in more slaty rock, he ob- 
tained slight impressions cf what appears to be Oldhamia antiqua, a 
fossil occurring abundantly at Bray Head and Carrick Mountain, and 
up to the present time confined to Irish localities. 
Professor Thomas Oldham} was the first to discover these remarkable 
fossils in the hard and fine-grained schists of Bray Head; they were 
afterwards described by Professor Edward Forbes as ‘‘the remains of 
marine animals, belonging either to Hydrozoa (corals), or Polyzoa (com- 
pound Mollusca’); and named by him Oldhamia, in honour of the dis- 
* On the Lower Paleozoic Rocks of the South-East of Ireland, by J. Beete Jukes, Esq., 
and the Rey. Professor Haughton. Trans. Royal Irish Acad., vol. xxiii., p. 563, (1859). 
+ Now Superintendent of the Geological Survey of India. 
