The surface of the clayey layer is slightly above high-water mark. About three-quarters of a mile to the westward, in the banks of a streamlet which forms the eastern limit of the extensive range of sand-dunes that stretches to Castlerock, the same zone is found to have changed to regular estuarine clay. The section now is The surface of the clay is three feet above high-water mark. It is a typical Scrobicularia deposit, yielding S. piperata, Mytilus edulis, Cardium edule, Tellina balthica, Littorina, and Hydrobia. A single perfect example of Tellina fabula, very rare as an estuarine clay fossil, occurred. Foraminifera were rather plentiful; among the rare species which occurred were Lagena distoma and L. pulchella. Between the two points described the estuarine zone was again seen, more sandy in character and with fewer shells, and covered by twelve feet of stratified yellow and brown sands, destitute of marine forms, and evidently the creation of the river during the epoch of submergence which has already been shown to have followed the Scrobicularia period. III.-LARNE Lough. The estuarine clays of Larne Lough could, until lately, be inspected at two points—at the old pottery at Larne; at the entrance to the lough, where building operations have now obscured them; and on the shore at Magheramorne, where good opportunities for their inspection still exist. The latter station is three miles above Larne, and the deposits probably extend continuously between, and still further up the lough. The character of the beds at the two spots indicated is widely different, but their relation to each other appears clear. (4.) Larne.-The Curran at Larne is a narrow sickle-shaped promontory a mile in length, rising at its highest point some twenty-five feet above high-water mark, and composed of stratified gravels with recent marine shells, resting on estuarine clay, as first pointed out by Gray. The clay was formerly used for the manufacture of pottery, and till lately could be seen in the excavations at the old factory, 1 Jour. Royal Hist. and Arch. Assoc. of Ireland, 4th Series, vol. v., No. 39, p. 130. whence samples examined by Wright1 yielded nearly seventy species of Foraminifera. At that point the clay is blackish and sandy, becoming more sandy below, and at least three feet thick. Six feet of marine gravels overlie it, and its surface is some six feet above highwater mark. Foraminifera plentiful. Characteristic shells-Tapes aureus, Tellina balthica, Scrobicularia piperata, Rissoa membranacea, Cerithium reticulatum. It will be seen by this description that this bed is essentially a lower or Scrobicularia clay. In the construction of a sewer along the road which passes the pottery, a section was exposed ten feet in depth, running north-east from the pottery to the sea. It was there seen that the surface of the clay sloped towards the water, and the gravels thinned out, and a bed of yellow sand with many shells was interposed, so that close to the beach the section was— The surface of the clay was now a few feet below high water mark. With the co-operation of Mr. William Gray, who was also engaged in investigations under a grant from the Academy, and the Belfast Naturalists' Field Club, excavations were undertaken, and a careful examination made of the Curran deposits at another point where the gravel beds are thickest, the spot selected being the escarpment of gravel on the southern side of the railway, 400 yards from the edge of the wharf by the Curran railway station. The section here was as follows: * A full account of this exploration, with plates and tabulated lists of fossils, will be found in Proc. Belfast Nat. Field Club, 1889-90, pp. 198-210. The gravels contain burrowing bivalves still in the natural position, showing that they lived on the spot where they are now found, and that these deposits formed a sea-bed rather than a sea-beach. They are stratified throughout, the different beds having varying dips, and they contain shells and rude flint implements from top to base. The surface of the estuarine clay is here six inches above ordinary high-water mark. It will be seen that the Larne estuarine clay dips both north-east and south-east from the pottery, and I am inclined to think that the clay was originally deposited in this sloping position, since intertidal shells occur at the pottery much more abundantly than at the lower points. The clay obtained from the trial pit by the railway was blackish, with remains of Zostera and shells, among which Cyamium minutum, Cardium exiguum, Trochus cinerarius, Rissoa striata, and Skenea planorbis were conspicuously abundant. Foraminifera were plentiful in the clay, especially the genera Miliolina and Discorbina; Polymorphina concava and Orbulina universa were the most noteworthy forms. The underlying black sand yielded a similar fauna. The black gravel, the lowest bed reached, contained large rounded boulders, covered with Spirorbis and corallines so fresh-looking that when cleaned they might easily have been supposed to have been just brought from the neighbouring beach. Patella, which, as would be expected, is very rare as an estuarine clay fossil, was abundant in this bed, which, like the overlying gravels, was evidently an accumulation formed by tidal currents in shallow water. On account of the quantity of water encountered, the base of the gravel could not be reached, but a short distance to the northward the Boulder clay crops out, and in all probability it directly underlies the last-mentioned bed. (5) Magheramorne.-The bed at Magheramorne, on the western shore of the lough three miles above Larne, differs widely from the Larne clay, being essentially a Thracia or deep-water clay, and possessing a richer fauna than any other estuarine deposit that I know. The bed has probably a considerable area, and extends out into the sea, its surface slightly above low-water level. It would probably still lie concealed below its living mantle of Zostera were it not for the steady advance of a high spoil-bank from the adjoining chalk quarries, which, encroaching on the sea, has thrust the clay upward to a height of several feet above high-water mark all around its margin. The beds thus exposed are faulted and folded like old metamorphic rocks, and form an excellent object lesson on the effects of lateral pressure on plastic formations. This deposit was first described and its fossils enume rated by Stewart; and Wright has catalogued no less than seventytwo species of Foraminifera from it. Some additions to its fauna have been since published by the writer3 and Alfred Bell. Of its large and varied fauna, the following shells may be mentioned, which are characteristic species at Magheramorne, and either very rare in, or absent from any other estuarine clay in the district:--Lima hians, Mytilus modiolus, Venus casina, Tapes virgineus, Pectunculus glycymeris. The clay is typical in character--very fine, plastic, and blue in colour; owing to its disturbance, the relation of its various zones cannot be traced. Foraminifera are abundant, and the specimens usually of large size; the following rare species were met with :-Lagena striatopunctata, Nodosaria obliqua, Miliolina seminuda. Along the base of a second spoil-bank which lies to the west of Magheramorne railway station, the clay is exposed by the same agency, and is of different aspect. There are zones of bright blue clay full of Cardium exiguum, layers a foot thick almost composed of Zostera, thick beds of yellowish clay almost devoid of shells, and blackish gritty layers. Scrobicularia piperata, Mytilus edulis, Tellina balthica, and Mactra subtruncata occurred here, none of which I found at the east spoilbank. This clay is decidedly littoral in character, but whether it underlies, overlies, or replaces the interesting clay further east, there is no opportunity of determining. Another zone is exposed at the extremity of the eastern out-crop, almost entirely made up of thousands upon thousands of oyster shells, the pairs of valves being still in juxtaposition. The shells are pear-shaped, and average five inches long by three broad. The thickness of this great old oyster-bed cannot be determined, but it was considerable, and generation must have succeeded generation hundreds of times. The variety and exuberant growth of the estuarine clay shells has already been commented upon, and this is especially noticeable at Magheramorne, when compared with the present paucity of molluscan life in Larne Lough. While the fauna of the Magheramorne estuarine clay numbers over ninety species of mollusks, dredgings by the Belfast Dredging Committee in 18585 in Larne Lough yielded but 26 species, 17 of them in a dead state. Six of these 26 shells are absent from the Magheramorne clay. IV. BELFAST LOUGH. The estuarine clays in Belfast Lough have, on account of their proximity to local observers, and the excellent opportunities that extensive harbour works have afforded for their study, been examined on frequent occasions. Probably the earliest explorer was Dr. William Magee, who, in 1830, collected a number of species, including the rare Lima hians, when Prince's Dock was in course of construction, and supplied a list of the estuarine clay fauna to James Bryce's "Tables of Simple Minerals, Rocks, and Shells" (Belfast, 1831); but they are included in the list of the recent shells of Down, Antrim, and Derry, without distinction. In the supplement to Mac Adam's Paper a list of seventy estuarine clay species is given, which was supplied by Grainger, who was then diligently exploring the deposits. A few species of mollusks obtained by William Thompson, in the clays about Belfast Harbour, are recorded in vol. iv. of his "Natural History of Ireland" (1856); and a collection of forty species, made by the same eminent naturalist at Belfast, is preserved in the museum of the Belfast Natural History and Philosophical Society. Hyndman, in the "First Report of the Belfast Dredging Committee," notes the occurrence of twenty-four species in the "alluvium." In 1858, Canon (then Mr.) Grainger contributed to the Dublin University Zoological and Botanical Association a valuable Paper, "On the Shells found in the Post-tertiary Deposits of Belfast," which was published in the Natural History Review for the following year. This author had previously contributed to Mac Adam's Paper, already mentioned, a list of the shells found in the Belfast bed, and had read at the meeting of the British Association at Belfast, in 1852, a Paper enumerating the species observed up to that date. This final Paper gives a list, with copious annotations, of 102 species, of which 96 are Mollusca. The shells were obtained from excavations made during the construction of the Victoria Channel, from the sand and mud raised for the railway embankments on either side of the bay, from sandy mud raised by steam dredges from the "bed of the present channel, near the lighthouse," and from raised beaches at Jordanstown and Holywood. The raised beaches do not belong to the estuarine clays. The geological position (if any) of the lighthouse-bed is indeterminable, but its fauna shows that it also does not belong to the series with which the present Paper 1 Report of British Association, 1857. |