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The total fauna enumerated in the present report numbers 342 species, divided as follows :Foraminifera, .
114 species. Echinoidea,
. . . . . 3
. . . . . . 31
. . . . . 3 ,
Total, . . . 342 The Foraminifera have been most carefully scrutinized by Mr. Joseph Wright, F.G.s., and the table of distribution may be taken as exhaustive; the same cannot yet be said of the Ostracoda, which require further examination. The apparent complete absence of Polyzoa is noteworthy. Echinoderms are few, as would be expected on a muddy and rather shallow bottom. Gastropods number 103 species, and Lamellibranchs 78. The present molluscan fauna of the North of Ireland includes 173 Gastropods and 120 Lamellibranchs ; the proportion of species of both univalves and bivalves of the estuarine clays, as compared with our present fauna, is therefore about two-thirds. Nine Gastropods and four Lamellibranchs occur in the estuarine deposits which are not known as recent species in the same area; if “recent species” were held to mean such species as had been dredged alive in the district, the above numbers would be very largely increased, particularly as regards the Gastropoda.
The proportion of marine Gastropoda to Lamellibranchs varies a good deal at the different stations. At Eglinton, Limavady Junction, and Alexandra Dock the ratio is exactly 1 to 1, there being respectively 27, 31, and 49 species of each order present. At the West Bank there are 36 univalves to 23 bivalves; at Magheramorne, 50 to 41; at Downpatrick, 32 to 14. In the Scrobicularia clays this ratio is reversed, Lamellibranchs being in a majority. Thus at the Bann there are 5 Gastropods to 14 Lamellibranchs; Albert Bridge, 7 to 16; and Newcastle, 6 to 12. In the total fauna the Gastropods are in a decided majority-103 to 78; but the Lamellibranchs are more generally distributed, so that the total number of occurrences of the various species of both orders in the different beds is much more equal ; a number of the univalves appear at only one or two stations.
As regards the more important genera, Rissoæ are well represented in the estuarine clays, 15 out of the 20 recent North of Ireland species being present; of Odostomiæ, there are 15, out of 21 species taken in Ulster waters. The genus Trophon is absent from the clays, and Defranciæ and Pleurotomæ are rare. Of bivalves, we note that Venus and Tapes are over-represented, and that Astarte is completely absent. Compared with the fauna of the underlying Glacial beds, we observe that the genera Leda, Astarte, and Trophon, which (with the exception of one valve of Leda minuta) are entirely absent from the estuarine series, are abundantly represented in the Glacial beds, in which also Venus and Tapes are very rare.
The previous papers and references concerning the North-east of Ireland estuarine clays are mentioned under the head of the deposits to which they refer, but the more important may be enumerated here.
The papers describing any of the beds or their fauna in detail are :
JAMES Mac ADAM—" Observations on the Neighbourhood of Belfast, with a description of the Cuttings on the Belfast and Co. Down Railway"; and Supplement to the same Paper. Journal of the Geological Society of Dublin, vol. IV., part ii., No. 2. Contains a list of estuarine clay species, supplied by Grainger.
J. GRAINGER" On the Shells found in the Alluvial Deposits of Belfast." Brit. Assoc. Report, 1852.
J. GRAINGER—“On the Shells found in the Post-tertiary Deposits of Belfast.” Nat. Hist. Review, 1859.
S. A. STEWART—"A List of the Fossils of the Estuarine Clays of the Counties of Down and Antrim.” Eighth Annual Report, Belfast Nat. Field Club, 1871, Appendix. Contains lists of the species observed in the Estuarine Clays of Belfast, Magheramorne, and Newtownards.
J. WRIGHT—"The Post-tertiary Foraminifera of the North-east of Ireland.” Proc. Belfast Nat. Field Club, 1879–80, Appendix. Contains list of Foraminifera found in the estuarine clays of Belfast, Magheramorne, Larne, Kircubbin, and Limavady Junction.
R. LL. PRAEGER—“On the Estuarine Clays at the new Alexandra Dock, Belfast.” Proc. Belfast Nat. Field Club, 1886–7, Appendix. Description of beds, and list of Foraminifera, Ostracoda, Mollusca, &c., observed in the excavations.
R. LL. PRAEGER—“Report of the Larne Gravels Committee." Proc. Belfast Nat. Field Club, 1889–90. Describes beds and molluscan fauna of the estuarine series at Larne.
A. BELL—"Fourth and final Report of the Committee ... appointed for the purpose of reporting upon the Manure Gravels of Wexford.” Brit. Assoc. Report, 1890. Contains a general description of the Belfast and Magheramorne beds, and list of Mollusca, chiefly drawn from the papers above enumerated.
Other references to the beds under consideration will be mentioned in the later pages of the present Report.
The district to which the present Report refers extends from Lon. donderry on the north to Dundalk on the south, and comprises the coast line of the counties of Londonderry, Antrim, Down, and the
northern half of Louth. In the tabular lists which follow, the distri. bution of fossils, in the various deposits, is shown by reference to seventeen stations, whose positions are laid down on the sketch-map on previous page, and which are thus distributed :
1 1. Eglinton.
7. Albert Bridge, Belfast.
8. Alexandra Dock, Belfast. 9. West Bank, Belfast Lough. 10. Holywood.
( 11. Newtownards.
( 13. Downpatrick.
The following notes describe these deposits in detail :
I.—Lough FOYLE. The Lough Foyle estuarine clays occupy an extensive area along the southern shore of the bay, stretching at least from the River Roe on the east to Culmore on the west, a distance of twelve miles, and attaining a known depth of twenty-five feet. The occurrence of these beds is mentioned by Portlock and Stewart, and their remarkably abundant Foraminifera catalogued by Wright from an examination of a large quantity of material obtained near the surface at Limavady Junction. For the purposes of the present inquiry, the beds were examined at two points.
(1). Eglinton.-Rather sandy light blue clay, obtained from three feet below the surface (which is at about high-water mark), by the railway a mile east of Eglinton Station. Shells very abundant. Characteristic species—Mactra subtruncata, Scrobicularia alba, Mya
1 Report on the Geology of the County of Londonderry, &c., pp. 161, 165. 2 Op. cit.
S Op. cit.
truncata, Turritella terebra, Utriculus obtusus, U. mammillatus. Three specimens occurred here of the beautiful Odostomia nitidissima-its only occurrence, so far as I am aware, as an Irish fossil. Foraminifera were plentiful.
(2). Limavady Junction.—The construction of a new railway bridge over the Burnfoot River supplied an excellent opportunity for the examination of the deposit. The iron caissons for the foundations were sunk through the clay to a depth of eighteen to twenty-five feet. The lowest third or fourth of this depth consisted of an estuarine clay of unusual character—a tough, firm, reddish brown clay, like a re-assorted Boulder clay, but full of Scrobicularia alba and Montacuta bidentata-characteristic estuarine species, which are absent from our Glacial beds. The rest of the deposit consisted of typical blue estuarine clay, its surface at about high-water mark, and containing many shells, of which Nucula nucleus, Scrobicularia alba, Corbula gibba, and Turritella terebra were especially abundant. The profusion of Turritella in the Lough Foyle estuarine clays is interesting in connexion with its profusion at an elevation of over 250 feet in Boulder clay at Bovevagh,' some eight miles southward, and its immense abundance on the shell-banks of Lough Foyle. Foraminifera were very abundant at this station, the genera Bulimina, Bolivina, and Lagena being well represented.
II.—RIVER BANN. Portlock writes3 “In Dunboe parish, on the boundary of Grange (More and Beg), is a bed of blue silt full of recent shells, Mytilus, Turbo, &c., in the banks of the stream, covered by 7 feet of fine sand (rabbit warren), the clay itself being 2 ft. 6 in. thick, and also resting on fine sand.” This place is on the southern bank of the Bann, about a mile from its mouth, where the Articlave River, which here forms the boundary of the two townlands mentioned, winds sluggishly through a sandy alluvial tract to join the larger river. On examining the banks of the stream, I found the following section :
taining Foraminifera, . .
Portlock, op. cit., pp. 157-159; and Stewart, “ Mollusca of the Boulder Clay of the North-east of Ireland,” Proc. Belfast Nat. Field Club, 1879-80, Appendix. 2 Portlock, op. cit. p. 163.
3 Op. cit. p. 161.