1869.] SEARLES WOOD—BOULDER-CLAY. 91
less clay of the north of Flamborough with a similar clay, also
wholly destitute of chalk, of which outliers cap the purple clay with
some chalk in Holderness, where, as at Dimlington and near Mappleton,
the cliff-section shows the Glacial series to have undergone
less denudation than elsewhere along that coast. We further
pointed out that the long-known fossiliferous bed of Bridlington
belonged to the Yorkshire Glacial formation; and we placed its
horizon immediately superior to the chalky clay (a)—that is
to say, in the lower part of the purple clay, wherein there is
chalk, and at the horizon indicated in the accompanying vertical
section (Pl. VII. fig. 1).
Now, while in Yorkshire we find the Glacial clay exhibiting the distinct feature of a gradual decrease and final disappearance of the chalk debris, succeeded by a deposit of considerable thickness, in which there is not a trace of chalk, the whole of the beds of the east and east centre of England indicate not only that debris from the chalk prevails throughout the series, but that it is to the full as copious in the uppermost layer that denudation has spared of the highest member of the series there as it is in the lowest.
It is therefore only with the highest member of that series, the common wide-spread Boulder-clay of East Anglia, that I propose to discuss the relationship borne by the Yorkshire Boulder-clay. As regards the very considerable and, I think, important series of deposits which are older than this wide-spread Boulder-clay, but are absent in Yorkshire and the north, I shall only have occasion to refer to them to the extent of pointing out the great distinction existing between their fauna and that of the bed at Bridlington, and of indicating their place in the vertical section accompanying this paper, as the structure and distribution of these older series will, I hope, form the subject of a future communication by myself and Mr. F. W. Harmer, F.G.S.,who has cooperated with me in working them out.
The particulars of the considerable fauna obtained from Bridlington, and of the fauna collected from the Middle and Lower Glacial deposits of East Anglia, have received much attention from my father, and they will be tabulated by him with the fauna from the several horizons of the Crag and from the Postglacial beds of the eastern side of England, in his supplement to the Monograph of the Crag Mollusca. In the meantime, however, for the purposes of this paper, and to show, on the one hand, how entirely distinct these deposits are in their palaeontological aspects from that of Bridlington, and, on the other, how closely they are connected in those aspects with the Crag, the following list, embodying our results up to the present time, as far as they concern the beds under consideration here, has been revised by him*:—
- The fauna of the Lower Glacial has been obtained with the assistance of
Mr. Harmer, and that of the Middle Glacial with the same assistance and with that of Mr. E. T. Dowson, of Geldeston; while Mr. Leckenby has rendered my father most valuable assistance in verifying the Bridlington shells.
