2

minor details, but sands and gravels dominate. Another boulder clay follows, which, however, is better displayed on the Holderness coast. Here also the lower clay (called by Mr. Lamplugh the "Basement Clay ") may be recognised, and we can distinguish in some places at least three masses of boulder clay, separated by beds of sand or gravel, which occasionally suggest the possibility of yet further subdivision. The upper mass of boulder clay, which in Holderness is distinctly reddish in colour, was distinguished by Mr. S. V. Wood, jun., as the Purple Clay.1 Fragments are less numerous in it than in the Basement Clay. As to the correlation of these deposits with those on the Norfolk coast, different opinions have been held. Lamplugh considers the "Basement Clay " the equivalent of the "Cromer Till" in the "Lower Glacial Deposits" of that district, and the Purple Clay as nearly on the horizon of the "Chalky" or "Upper Boulder Clay" of East Anglia. Though the lithological differences between these deposits are considerable, there is very much to be said in favour of this view. authors have distinguished a Hessle Sand and a Hessle (Boulder) Clay in parts of Yorkshire, and have placed these at a higher level than the Purple Clay; but Mr.

1 Quart. Jour. Geol. Soc., xxiv. (1868), p. 146.

Mr.

Many

2 In the latter, shells, whole and broken, are sometimes not rare, and in it occur patches of sand containing molluscs, the bivalves often having their valves united. These have been called the Bridlington Crag. Mr. Lamplugh is of opinion that these shelly sands were not formed in situ, but are of the nature of erratics.

1

Jukes-Browne has shown, and with this view Mr. Lamplugh concurs, that not only is this subdivision. of merely local value, but also the "Hessle " deposits generally are hardly separable from the Purple Clay.

On the other side of the Humber similar sections occur, but are not generally so well displayed; in short, the glacial deposits of North-East England are a group of boulder clays, and of gravels or sands, the former on the whole predominating, and the latter being more persistent towards the middle part. These gravels and sands must have been deposited under water, and they not seldom indicate the action of fairly rapid currents. show no signs of stratification; at others they have a laminated structure, the included fragments also suggesting a certain regularity of disposition, while now and again distinct interlaminations of more sandy materials occur. In other words, nothing is found irreconcilable with the idea that the clays also were formed under water, while certain phenomena require explanation if the materials were deposited on a land surface which generally was occupied by ice.

The boulder clays sometimes

Before leaving this subject attention may be directed to a rather remarkable line of hills which crosses the peninsula of Flamborough Head, running from Beacon Hill northward to Sanwick, and then continuing for some miles farther, roughly parallel with and a short distance from the coast, till it sinks into the glacial

1 Quart. Jour. Geol. Soc., xli. (1885), p. 114.

deposits occupying the Vale of Pickering.

The range

at first is gently undulating, but it becomes more defi

FIG. 17.-Supposed Moraine between Speeton and Flamborough.

nitely ridge-shaped in the neighbourhood of Speeton
village. The hills, as is shown in the coast sections,
are composed of sands, gravels, and clays; stratified,

doubtless, though somewhat irregularly, and exhibiting often the peculiar structure called "arched bedding." 1 Of late years these hills have been frequently claimed as remnants of the right lateral moraine of a glacier which occupied the bed of the North Sea and trespassed on the Yorkshire coast, but their resemblance externally to a moraine is not striking, and their internal structures are totally different.2

The glacial deposits of the north-west of England, as far south as parts of Cheshire and North Wales, admit in some places of a tripartite division, viz., a Lower Boulder Clay, Intermediate Sands and Gravels, and an Upper Boulder Clay. This division, however, as in the eastern counties, cannot always be maintained, and the middle member is sometimes wanting, the one boulder clay shading into the other, so that they can hardly be distinguished. The first, according to Mr. H. B. Woodward's 3 is a summary,

"stiff

1 That is to say, the component layers, though often irregular and lenticular, are arranged in rude symmetry with the outer surface, or at any rate in a series of more or less concentric curves.

2 Moraine deposits (due to land-ice) are practically unstratified. Traces of stratification may be now and then detected, just as in any talus heap, and probably from the same cause (a slight packing or shifting of the material in process of time); but these are faint, rare, and local, so far as my experience goes, and it is by no means small. Certain cases which have been quoted to prove the contrary from America are not conclusive, because the origin of these deposits is open to question. "Arched bedding" would be a very improbable structure in a moraine. Its cross-section should exhibit (if anything) either a series of inverted Vs broadening from the apex, or groups of bands parallel to one side, the latter being the less improbable.

"Geology of England and Wales," p. 48.

reddish-brown clay, with subordinate beds of laminated loam, seams and pockets of sand, stones and many large boulders. . . . The lowest portion of the accumulation is a blue or bluish-grey stony clay with many scratched boulders." The maximum thickness of the whole deposit is about 120 feet, but it is generally much less. "The Middle Drift consists of fine sands and gravel with subordinate beds of clay and loam, the whole in general distinctly stratified, but frequently contorted; " the maximum thickness. (at Kersal Moor on the west of Manchester) being 200 feet. "The Upper Boulder Clay consists of reddish-brown clay, with grey and blue partings, and glaciated stones and boulders. It sometimes contains bands of sand and finely laminated clay," and attains a thickness of about 100 feet as a maximum. But the total thickness of the three deposits, when they occur in the same area, is rarely more than from 150 to 200 feet.1

The Cumbrian mountains and the adjacent lofty fells of the Pennine Range obviously have been occupied by glaciers, for among them ice-worn rocks, moraines, and perched blocks are common. During part of the time the glaciers, at any rate in the former district, must have descended very near to, if not below, the present sea-level. Here the older

1 Foraminifers and ostracods have been found in the two boulder clays, and molluscs in all the deposits (sometimes rather abundantly in the sands), lists of which are given by Mr. W. Shone, Quart. Jour. Geol. Soc., xxxiv. (1878), p. 383.