Fig. 452, and found by Mr. G. H. Gaviller in gravel dug at Hackney Down, to the north-east of London, and not far from Shacklewell. It is of ochreous flint, slightly rolled, and in form remarkably like that from Bournemouth, Fig. 476. Though the exact place whence it came is unknown, there can be no doubt of its belonging to the Hackney Down gravels, which may be regarded as identical in age and character with those of Shacklewell, which have been described by Sir Joseph Prestwich.[1] The surface of the ground at Hackney Down[2] is 70 feet above Ordnance Datum, and in 1806 a shaft was there sunk through gravel and sand, to a depth of 22 feet. In the sandy beds at the base Mr. G. J. Smith[3] discovered numerous land and freshwater shells, and among them the Hydrobia marginata—already mentioned as having been found in the Bedford Drift, and as being no longer an inhabitant of Britain—and the Corbicula fluminalis, which has already been cited as occurring near Cambridge, and of which more will be said immediately. The Shacklewell gravel mainly consists of sub-angular broken flints, some large flints but little worn, Lower Tertiary pebbles, a few quartz and sandstone pebbles, and some rolled blocks of hard Tertiary sandstone. In the pit described by Sir Joseph Prestwich there is, at a depth of about 8 feet, a bed of sandy clay intercalated in the gravel, and containing mammalian remains, numerous land and freshwater shells, and remains of oak, elm, alder, and hazel. The group of shells procured here resembles that of the Salisbury Drift, of which mention will be made hereafter.
Since 1854, when his paper was read, numerous specimens of the Corbicula fluminalis, or, as it was formerly called, the Cyrena consobrina, have been found here by Sir Joseph Prestwich, Sir Charles Lyell,[4] and others, including myself. This shell, of a mollusc no longer living in Europe, though still found in the Nile and in several Asiatic rivers, has also been found in the Drift deposits of the Somme at Menchecourt, near Abbeville, associated with flint implements; and is likewise to be met with in the drift deposits of the Thames at Gray's Thurrock, Ilford, Erith, and Crayford, in several of which implements have now been found. The beds at these places have by some geologists been regarded as belonging to an older and Pre-glacial period; but the discovery of an implement at Hackney Down raises a presumption that the gravel there is, like other flint implement-bearing gravels. Post-glacial; and the discovery of an implement in beds of fluviatile origin at a still higher level than those of Hackney Down corroborates this view, as the lower bed is probably the more modern.
The fluviatile beds in question were exposed in two brick-pits at Highbury New Park, near Stoke Newington, and attention was first called to them in August, 1868,[5] by the late Mr. Alfred Tylor, F.G.S. The surface of the ground at the more eastern of these two pits is, according to Mr. Tylor, 102 feet above Ordnance Datum; and 22 feet below the surface there is a bed of clay 2 feet thick, full of land and freshwater shells, accompanied by much wood. There are
